{"id":93922,"date":"2026-04-12T19:05:14","date_gmt":"2026-04-12T12:05:14","guid":{"rendered":"https:\/\/itviec.com\/blog\/?p=93922"},"modified":"2026-04-12T20:57:07","modified_gmt":"2026-04-12T13:57:07","slug":"ke-thua-trong-java","status":"publish","type":"post","link":"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/","title":{"rendered":"K\u1ebf th\u1eeba trong Java: Kh\u00e1i ni\u1ec7m, ph\u00e2n lo\u1ea1i v\u00e0 nh\u1eefng l\u01b0u \u00fd"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">N\u1ed9i dung b\u00e0i vi\u1ebft<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Cach_hoat_dong_cua_ke_thua_trong_Java\" >C\u00e1ch ho\u1ea1t \u0111\u1ed9ng c\u1ee7a k\u1ebf th\u1eeba trong Java<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Cu_phap_cua_ke_thua_trong_Java_voi_tu_khoa_extends\" >C\u00fa ph\u00e1p c\u1ee7a k\u1ebf th\u1eeba trong Java v\u1edbi t\u1eeb kh\u00f3a extends<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Cac_loai_ke_thua_trong_Java\" >C\u00e1c lo\u1ea1i k\u1ebf th\u1eeba trong Java<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Tai_sao_Java_khong_ho_tro_da_ke_thua_voi_Class\" >T\u1ea1i sao Java kh\u00f4ng h\u1ed7 tr\u1ee3 \u0111a k\u1ebf th\u1eeba v\u1edbi Class?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Tu_khoa_super_va_Ghi_de_phuong_thuc_Method_Overriding\" >T\u1eeb kh\u00f3a super v\u00e0 Ghi \u0111\u00e8 ph\u01b0\u01a1ng th\u1ee9c (Method Overriding)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Nhung_thanh_phan_khong_duoc_ke_thua_trong_Java\" >Nh\u1eefng th\u00e0nh ph\u1ea7n kh\u00f4ng \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba trong Java<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Khi_nao_nen_dung_ke_thua\" >Khi n\u00e0o n\u00ean d\u00f9ng k\u1ebf th\u1eeba?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Cac_cau_hoi_thuong_gap_ve_ke_thua_trong_Java\" >C\u00e1c c\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p v\u1ec1 k\u1ebf th\u1eeba trong Java<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/#Ket_luan\" >K\u1ebft lu\u1eadn<\/a><\/li><\/ul><\/nav><\/div>\n\n<p><strong><em>K\u1ebf th\u1eeba (Inheritance) trong Java l\u00e0 c\u01a1 ch\u1ebf cho ph\u00e9p m\u1ed9t l\u1edbp con s\u1edf h\u1eefu l\u1ea1i to\u00e0n b\u1ed9 c\u00e1c thu\u1ed9c t\u00ednh v\u00e0 ph\u01b0\u01a1ng th\u1ee9c t\u1eeb l\u1edbp cha, gi\u00fap t\u1ed1i \u01b0u h\u00f3a vi\u1ec7c t\u00e1i s\u1eed d\u1ee5ng m\u00e3 ngu\u1ed3n (Reusability). Vi\u1ec7c \u00e1p d\u1ee5ng k\u1ebf th\u1eeba c\u1ea7n s\u1ef1 t\u00ednh to\u00e1n k\u1ef9 l\u01b0\u1ee1ng \u0111\u1ec3 tr\u00e1nh t\u1ea1o ra c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p qu\u00e1 ph\u1ee9c t\u1ea1p v\u00e0 kh\u00f3 b\u1ea3o tr\u00ec.<\/em><\/strong><\/p>\n\n\n\n<p>\u0110\u1ecdc b\u00e0i vi\u1ebft \u0111\u1ec3 hi\u1ec3u th\u00eam v\u1ec1:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>C\u00fa ph\u00e1p v\u00e0 c\u00e1ch ho\u1ea1t \u0111\u1ed9ng c\u1ee7a k\u1ebf th\u1eeba trong Java<\/li>\n\n\n\n<li>C\u00e1c lo\u1ea1i k\u1ebf th\u1eeba trong Java<\/li>\n\n\n\n<li>T\u1ea1i sao Java kh\u00f4ng h\u1ed7 tr\u1ee3 \u0111a k\u1ebf th\u1eeba v\u1edbi Class?<\/li>\n\n\n\n<li>T\u1eeb kh\u00f3a super v\u00e0 ghi \u0111\u00e8 ph\u01b0\u01a1ng th\u1ee9c (Method Overriding)<\/li>\n\n\n\n<li>Nh\u1eefng th\u00e0nh ph\u1ea7n kh\u00f4ng \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba<\/li>\n\n\n\n<li>Khi n\u00e0o n\u00ean d\u00f9ng k\u1ebf th\u1eeba?<\/li>\n\n\n\n<li>C\u00e1c c\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p v\u1ec1 k\u1ebf th\u1eeba trong Java<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-cach-ho\u1ea1t-d\u1ed9ng-c\u1ee7a-k\u1ebf-th\u1eeba-trong-java\"><span class=\"ez-toc-section\" id=\"Cach_hoat_dong_cua_ke_thua_trong_Java\"><\/span><strong>C\u00e1ch ho\u1ea1t \u0111\u1ed9ng c\u1ee7a k\u1ebf th\u1eeba trong Java<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u00dd t\u01b0\u1edfng c\u1ee7a k\u1ebf th\u1eeba r\u1ea5t th\u1ef1c t\u1ebf: Khi b\u1ea1n c\u1ea7n t\u1ea1o m\u1ed9t l\u1edbp m\u1edbi nh\u01b0ng \u0111\u00e3 c\u00f3 s\u1eb5n m\u1ed9t l\u1edbp kh\u00e1c ch\u1ee9a m\u1ed9t ph\u1ea7n m\u00e3 ngu\u1ed3n b\u1ea1n mong mu\u1ed1n, b\u1ea1n c\u00f3 th\u1ec3 cho l\u1edbp m\u1edbi k\u1ebf th\u1eeba l\u1ea1i l\u1edbp \u0111\u00f3. Vi\u1ec7c n\u00e0y cho ph\u00e9p b\u1ea1n s\u1eed d\u1ee5ng l\u1ea1i c\u00e1c tr\u01b0\u1eddng d\u1eef li\u1ec7u v\u00e0 ph\u01b0\u01a1ng th\u1ee9c \u0111\u00e3 c\u00f3 m\u00e0 kh\u00f4ng c\u1ea7n t\u1ed1n c\u00f4ng vi\u1ebft l\u1ea1i hay ki\u1ec3m th\u1eed t\u1eeb \u0111\u1ea7u.<\/p>\n\n\n\n<p>C\u01a1 ch\u1ebf n\u00e0y \u0111\u01b0\u1ee3c x\u00e2y d\u1ef1ng d\u1ef1a tr\u00ean m\u1ed1i quan h\u1ec7 &#8220;IS-A&#8221; (l\u00e0 m\u1ed9t), v\u00ed d\u1ee5 nh\u01b0 &#8220;Xe h\u01a1i l\u00e0 m\u1ed9t Ph\u01b0\u01a1ng ti\u1ec7n&#8221; hay &#8220;L\u1eadp tr\u00ecnh vi\u00ean l\u00e0 m\u1ed9t Nh\u00e2n vi\u00ean&#8221;.<\/p>\n\n\n\n<p>V\u1ec1 m\u1eb7t k\u1ef9 thu\u1eadt, m\u1ed9t l\u1edbp con s\u1ebd th\u1eeba h\u01b0\u1edfng t\u1ea5t c\u1ea3 c\u00e1c th\u00e0nh vi\u00ean (bi\u1ebfn, ph\u01b0\u01a1ng th\u1ee9c v\u00e0 l\u1edbp l\u1ed3ng nhau) t\u1eeb l\u1edbp cha c\u1ee7a n\u00f3. Trong l\u1eadp tr\u00ecnh Java, c\u00e1c th\u00e0nh ph\u1ea7n n\u00e0y th\u01b0\u1eddng \u0111\u01b0\u1ee3c g\u1ecdi b\u1eb1ng c\u00e1c c\u1eb7p t\u00ean sau:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>L\u1edbp cha:<\/strong> Parent Class, Super Class ho\u1eb7c Base Class.<\/li>\n\n\n\n<li><strong>L\u1edbp con:<\/strong> Child Class, Sub Class ho\u1eb7c Derived Class.<\/li>\n<\/ul>\n\n\n\n<p>Tuy nhi\u00ean, b\u1ea1n c\u1ea7n l\u01b0u \u00fd r\u1eb1ng <strong>Constructor (h\u00e0m kh\u1edfi t\u1ea1o) kh\u00f4ng \u0111\u01b0\u1ee3c coi l\u00e0 th\u00e0nh vi\u00ean<\/strong>, v\u00ec v\u1eady ch\u00fang kh\u00f4ng \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba tr\u1ef1c ti\u1ebfp. Thay v\u00e0o \u0111\u00f3, l\u1edbp con s\u1ebd g\u1ecdi \u0111\u1ebfn Constructor c\u1ee7a l\u1edbp cha khi c\u1ea7n thi\u1ebft.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p><em>\u0110\u1ecdc th\u00eam: <strong><a href=\"https:\/\/itviec.com\/blog\/java-la-gi\/\" target=\"_blank\" rel=\"noreferrer noopener\">Java l\u00e0 g\u00ec? T\u1ea5t c\u1ea3 nh\u1eefng \u0111i\u1ec1u b\u1ea1n c\u1ea7n bi\u1ebft v\u1ec1 ng\u00f4n ng\u1eef Java<\/a><\/strong><\/em><\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-cu-phap-c\u1ee7a-k\u1ebf-th\u1eeba-trong-java-v\u1edbi-t\u1eeb-khoa-extends\"><span class=\"ez-toc-section\" id=\"Cu_phap_cua_ke_thua_trong_Java_voi_tu_khoa_extends\"><\/span><strong>C\u00fa ph\u00e1p c\u1ee7a k\u1ebf th\u1eeba trong Java v\u1edbi t\u1eeb kh\u00f3a <\/strong><strong>extends<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>\u0110\u1ec3 thi\u1ebft l\u1eadp m\u1ed1i quan h\u1ec7 n\u00e0y, Java s\u1eed d\u1ee5ng t\u1eeb kh\u00f3a <code>extends<\/code>. B\u1ea1n c\u00f3 th\u1ec3 tham kh\u1ea3o chi ti\u1ebft h\u01a1n v\u1ec1 c\u00e1c quy t\u1eafc v\u00e0 gi\u1edbi h\u1ea1n t\u1ea1i b\u00e0i vi\u1ebft<a href=\"https:\/\/www.google.com\/search?q=link-den-bai-viet-cua-ban&amp;authuser=1\"><\/a>T\u1eeb kh\u00f3a extends trong Java.<\/p>\n\n\n\n<p>V\u00ed d\u1ee5 minh h\u1ecda:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ L\u1edbp cha (Super Class)\nclass Animal {\n    void eat() {\n        System.out.println(\"\u0110ang \u0103n...\");\n    }\n}\n\n\/\/ L\u1edbp con (Sub Class) th\u1eeba h\u01b0\u1edfng t\u1eeb Animal\nclass Dog extends Animal {\n    void bark() {\n        System.out.println(\"G\u00e2u g\u00e2u!\");\n    }\n}\n\npublic class Main {\n    public static void main(String&#91;] args) {\n        Dog myDog = new Dog();\n        \n        \/\/ S\u1eed d\u1ee5ng ph\u01b0\u01a1ng th\u1ee9c th\u1eeba h\u01b0\u1edfng t\u1eeb l\u1edbp Animal\n        myDog.eat(); \n        \n        \/\/ S\u1eed d\u1ee5ng ph\u01b0\u01a1ng th\u1ee9c ri\u00eang c\u1ee7a l\u1edbp Dog\n        myDog.bark();\n    }\n}<\/code><\/pre>\n\n\n\n<p>\u1ede v\u00ed d\u1ee5 n\u00e0y, d\u00f9 l\u1edbp <code>Dog<\/code> kh\u00f4ng khai b\u00e1o ph\u01b0\u01a1ng th\u1ee9c <code>eat()<\/code>, \u0111\u1ed1i t\u01b0\u1ee3ng <code>myDog<\/code> v\u1eabn th\u1ef1c hi\u1ec7n \u0111\u01b0\u1ee3c h\u00e0nh \u0111\u1ed9ng n\u00e0y nh\u1edd v\u00e0o c\u01a1 ch\u1ebf k\u1ebf th\u1eeba t\u1eeb <code>Animal<\/code>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-cac-lo\u1ea1i-k\u1ebf-th\u1eeba-trong-java\"><span class=\"ez-toc-section\" id=\"Cac_loai_ke_thua_trong_Java\"><\/span><strong>C\u00e1c lo\u1ea1i k\u1ebf th\u1eeba trong Java<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Java h\u1ed7 tr\u1ee3 ba ki\u1ec3u k\u1ebf th\u1eeba ch\u00ednh d\u1ef1a tr\u00ean giai c\u1ea5p c\u1ee7a l\u1edbp (Class). Vi\u1ec7c ph\u00e2n lo\u1ea1i n\u00e0y gi\u00fap b\u1ea1n t\u1ed5 ch\u1ee9c c\u1ea5u tr\u00fac \u0111\u1ed1i t\u01b0\u1ee3ng m\u1ed9t c\u00e1ch logic v\u00e0 khoa h\u1ecdc:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u0110\u01a1n k\u1ebf th\u1eeba (Single Inheritance):<\/strong> M\u1ed9t l\u1edbp con ch\u1ec9 k\u1ebf th\u1eeba tr\u1ef1c ti\u1ebfp t\u1eeb duy nh\u1ea5t m\u1ed9t l\u1edbp cha. \u0110\u00e2y l\u00e0 ki\u1ec3u ph\u1ed5 bi\u1ebfn nh\u1ea5t, \u0111\u1ea3m b\u1ea3o t\u00ednh \u0111\u01a1n gi\u1ea3n v\u00e0 r\u00f5 r\u00e0ng c\u1ee7a m\u00e3 ngu\u1ed3n.<\/li>\n\n\n\n<li><strong>K\u1ebf th\u1eeba \u0111a c\u1ea5p (Multilevel Inheritance):<\/strong> T\u1ea1o ra m\u1ed9t chu\u1ed7i k\u1ebf th\u1eeba theo d\u1ea1ng &#8220;\u00f4ng &#8211; cha &#8211; con&#8221;. V\u00ed d\u1ee5: L\u1edbp C k\u1ebf th\u1eeba l\u1edbp B, l\u1edbp B l\u1ea1i k\u1ebf th\u1eeba t\u1eeb l\u1edbp A. L\u00fac n\u00e0y, l\u1edbp C s\u1ebd s\u1edf h\u1eefu \u0111\u1eb7c t\u00ednh c\u1ee7a c\u1ea3 A v\u00e0 B.<\/li>\n\n\n\n<li><strong>K\u1ebf th\u1eeba th\u1ee9 b\u1eadc (Hierarchical Inheritance):<\/strong> Nhi\u1ec1u l\u1edbp con c\u00f9ng k\u1ebf th\u1eeba chung t\u1eeb m\u1ed9t l\u1edbp cha. V\u00ed d\u1ee5: C\u1ea3 l\u1edbp <code>Dog<\/code> v\u00e0 <code>Cat<\/code> \u0111\u1ec1u c\u00f9ng k\u1ebf th\u1eeba t\u1eeb l\u1edbp <code>Animal<\/code>.<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"553\" height=\"287\" src=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-1.png\" alt=\"\" class=\"wp-image-93923\" srcset=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-1.png 553w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-1-300x156.png 300w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-1-200x104.png 200w\" sizes=\"auto, (max-width: 553px) 100vw, 553px\" \/><\/figure>\n\n\n\n<p class=\"has-text-align-center\"><em>S\u01a1 \u0111\u1ed3 c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p c\u00e1c l\u1edbp (Class Hierarchy) k\u1ebf th\u1eeba t\u1eeb l\u1edbp Object.<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-t\u1ea1i-sao-java-khong-h\u1ed7-tr\u1ee3-da-k\u1ebf-th\u1eeba-v\u1edbi-class\"><span class=\"ez-toc-section\" id=\"Tai_sao_Java_khong_ho_tro_da_ke_thua_voi_Class\"><\/span><strong>T\u1ea1i sao Java kh\u00f4ng h\u1ed7 tr\u1ee3 \u0111a k\u1ebf th\u1eeba v\u1edbi Class?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Nhi\u1ec1u ng\u00f4n ng\u1eef nh\u01b0 C++ cho ph\u00e9p m\u1ed9t l\u1edbp k\u1ebf th\u1eeba t\u1eeb nhi\u1ec1u l\u1edbp cha c\u00f9ng l\u00fac. Tuy nhi\u00ean, Java \u0111\u00e3 lo\u1ea1i b\u1ecf kh\u1ea3 n\u0103ng n\u00e0y <strong>\u0111\u1ec3 tr\u00e1nh v\u1ea5n \u0111\u1ec1 &#8220;Kim c\u01b0\u01a1ng&#8221; (Diamond Problem)<\/strong>.<\/p>\n\n\n\n<p>H\u00e3y t\u01b0\u1edfng t\u01b0\u1ee3ng n\u1ebfu l\u1edbp C c\u00f9ng k\u1ebf th\u1eeba t\u1eeb l\u1edbp <code>A<\/code> v\u00e0 l\u1edbp <code>B<\/code>. N\u1ebfu c\u1ea3 <code>A<\/code> v\u00e0 <code>B<\/code> \u0111\u1ec1u c\u00f3 m\u1ed9t ph\u01b0\u01a1ng th\u1ee9c gi\u1ed1ng h\u1ec7t t\u00ean nhau nh\u01b0ng c\u00e1ch x\u1eed l\u00fd kh\u00e1c nhau, Java s\u1ebd kh\u00f4ng th\u1ec3 x\u00e1c \u0111\u1ecbnh l\u1edbp C n\u00ean s\u1eed d\u1ee5ng ph\u01b0\u01a1ng th\u1ee9c c\u1ee7a b\u00ean n\u00e0o. \u0110i\u1ec1u n\u00e0y g\u00e2y ra s\u1ef1 nh\u1eadp nh\u1eb1ng v\u00e0 ti\u1ec1m \u1ea9n l\u1ed7i nghi\u00eam tr\u1ecdng trong h\u1ec7 th\u1ed1ng.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-gi\u1ea3i-phap-s\u1eed-d\u1ee5ng-interface\"><strong>Gi\u1ea3i ph\u00e1p: S\u1eed d\u1ee5ng Interface<\/strong><\/h3>\n\n\n\n<p>\u0110\u1ec3 gi\u1ea3i quy\u1ebft nhu c\u1ea7u m\u1ed9t \u0111\u1ed1i t\u01b0\u1ee3ng c\u1ea7n mang \u0111\u1eb7c t\u00ednh c\u1ee7a nhi\u1ec1u ngu\u1ed3n kh\u00e1c nhau, Java cung c\u1ea5p <strong>Interface<\/strong>. M\u1ed9t l\u1edbp ch\u1ec9 c\u00f3 th\u1ec3 k\u1ebf th\u1eeba (extends) m\u1ed9t l\u1edbp cha, nh\u01b0ng c\u00f3 th\u1ec3 tri\u1ec3n khai (implements) kh\u00f4ng gi\u1edbi h\u1ea1n s\u1ed1 l\u01b0\u1ee3ng Interface.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-so-sanh-inheritance-class-va-interface\"><strong>So s\u00e1nh Inheritance (Class) v\u00e0 Interface<\/strong><\/h3>\n\n\n\n<p>D\u01b0\u1edbi \u0111\u00e2y l\u00e0 b\u1ea3ng so s\u00e1nh nhanh gi\u00fap b\u1ea1n ph\u00e2n bi\u1ec7t khi n\u00e0o n\u00ean d\u00f9ng k\u1ebf th\u1eeba l\u1edbp v\u00e0 khi n\u00e0o n\u00ean d\u00f9ng Interface:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>\u0110\u1eb7c \u0111i\u1ec3m<\/strong><\/td><td><strong>K\u1ebf th\u1eeba (Inheritance &#8211; Class)<\/strong><\/td><td><strong>Interface<\/strong><\/td><\/tr><tr><td>B\u1ea3n ch\u1ea5t<\/td><td>M\u1ed1i quan h\u1ec7 &#8220;IS-A&#8221; (L\u00e0 m\u1ed9t).<\/td><td>M\u1ed1i quan h\u1ec7 &#8220;CAN-DO&#8221; (C\u00f3 kh\u1ea3 n\u0103ng).<\/td><\/tr><tr><td>S\u1ed1 l\u01b0\u1ee3ng<\/td><td>Ch\u1ec9 \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba duy nh\u1ea5t 1 l\u1edbp cha.<\/td><td>C\u00f3 th\u1ec3 th\u1ef1c thi nhi\u1ec1u Interface c\u00f9ng l\u00fac.<\/td><\/tr><tr><td>M\u1ee5c \u0111\u00edch<\/td><td>T\u00e1i s\u1eed d\u1ee5ng m\u00e3 ngu\u1ed3n v\u00e0 chia s\u1ebb thu\u1ed9c t\u00ednh.<\/td><td>Thi\u1ebft l\u1eadp b\u1ed9 quy t\u1eafc (h\u00e0nh vi) chung.<\/td><\/tr><tr><td>Ph\u01b0\u01a1ng th\u1ee9c<\/td><td>C\u00f3 th\u1ec3 ch\u1ee9a c\u1ea3 ph\u01b0\u01a1ng th\u1ee9c tr\u1eebu t\u01b0\u1ee3ng v\u00e0 ph\u01b0\u01a1ng th\u1ee9c c\u00f3 th\u00e2n h\u00e0m.<\/td><td>Ch\u1ee7 y\u1ebfu ch\u1ee9a c\u00e1c ph\u01b0\u01a1ng th\u1ee9c tr\u1eebu t\u01b0\u1ee3ng (kh\u00f4ng c\u00f3 th\u00e2n h\u00e0m).<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>V\u00ed d\u1ee5 Code minh ho\u1ea1:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ 1. Interface \u0111\u1ecbnh ngh\u0129a \"Kh\u1ea3 n\u0103ng\" (CAN-DO)\ninterface Flyable {\n    void fly(); \/\/ Quy t\u1eafc: Ai th\u1ef1c thi interface n\u00e0y \u0111\u1ec1u ph\u1ea3i bi\u1ebft bay\n}\n\n\/\/ 2. L\u1edbp cha \u0111\u1ecbnh ngh\u0129a \"B\u1ea3n ch\u1ea5t\" (IS-A)\nabstract class Bird {\n    String name;\n    \n    Bird(String name) {\n        this.name = name;\n    }\n\n    void eat() {\n        System.out.println(name + \" \u0111ang \u0103n...\");\n    }\n    \n    abstract void makeSound(); \/\/ M\u1ed7i lo\u00e0i chim k\u00eau m\u1ed9t ki\u1ec3u kh\u00e1c nhau\n}\n\n\/\/ 3. L\u1edbp Eagle: K\u1ebf th\u1eeba 1 l\u1edbp v\u00e0 th\u1ef1c thi 1 Interface\nclass Eagle extends Bird implements Flyable {\n    Eagle(String name) {\n        super(name);\n    }\n\n    @Override\n    void makeSound() {\n        System.out.println(\"Ti\u1ebfng \u0111\u1ea1i b\u00e0ng: \u00c9c \u00e9c!\");\n    }\n\n    @Override\n    public void fly() {\n        System.out.println(name + \" \u0111ang bay l\u01b0\u1ee3n tr\u00ean b\u1ea7u tr\u1eddi cao.\");\n    }\n}\n\n\/\/ 4. L\u1edbp Penguin: Ch\u1ec9 k\u1ebf th\u1eeba l\u1edbp Bird (v\u00ec c\u00e1nh c\u1ee5t kh\u00f4ng bi\u1ebft bay)\nclass Penguin extends Bird {\n    Penguin(String name) {\n        super(name);\n    }\n\n    @Override\n    void makeSound() {\n        System.out.println(\"Ti\u1ebfng chim c\u00e1nh c\u1ee5t: C\u1ea1p c\u1ea1p!\");\n    }\n}\n\n\/\/ --- H\u00e0m Main \u0111\u1ec3 ch\u1ea1y th\u1eed ---\npublic class Main {\n    public static void main(String&#91;] args) {\n        Eagle myEagle = new Eagle(\"\u0110\u1ea1i b\u00e0ng v\u00e0ng\");\n        Penguin myPenguin = new Penguin(\"C\u00e1nh c\u1ee5t Pingu\");\n\n        \/\/ C\u1ea3 hai \u0111\u1ec1u c\u00f3 h\u00e0nh vi t\u1eeb l\u1edbp cha Bird\n        myEagle.eat();\n        myPenguin.eat();\n\n        \/\/ Ch\u1ec9 \u0110\u1ea1i b\u00e0ng m\u1edbi c\u00f3 kh\u1ea3 n\u0103ng bay (Interface)\n        myEagle.fly();\n        \n        \/\/ myPenguin.fly(); \/\/ L\u1ed7i bi\u00ean d\u1ecbch v\u00ec Penguin kh\u00f4ng implement Flyable\n    }\n}<\/code><\/pre>\n\n\n\n<p>Vi\u1ec7c k\u1ebft h\u1ee3p linh ho\u1ea1t gi\u1eefa k\u1ebf th\u1eeba l\u1edbp v\u00e0 Interface ch\u00ednh l\u00e0 ch\u00eca kh\u00f3a \u0111\u1ec3 t\u1ea1o ra nh\u1eefng h\u1ec7 th\u1ed1ng Java v\u1eeba ch\u1eb7t ch\u1ebd, v\u1eeba linh ho\u1ea1t.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-t\u1eeb-khoa-super-va-ghi-de-ph\u01b0\u01a1ng-th\u1ee9c-method-overriding\"><span class=\"ez-toc-section\" id=\"Tu_khoa_super_va_Ghi_de_phuong_thuc_Method_Overriding\"><\/span><strong>T\u1eeb kh\u00f3a <\/strong><strong>super<\/strong><strong> v\u00e0 Ghi \u0111\u00e8 ph\u01b0\u01a1ng th\u1ee9c (Method Overriding)<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Khi l\u00e0m vi\u1ec7c v\u1edbi k\u1ebf th\u1eeba, kh\u00f4ng ph\u1ea3i l\u00fac n\u00e0o l\u1edbp con c\u0169ng s\u1eed d\u1ee5ng nguy\u00ean b\u1ea3n nh\u1eefng g\u00ec l\u1edbp cha cung c\u1ea5p. \u0110\u00f4i khi, b\u1ea1n c\u1ea7n tham chi\u1ebfu ng\u01b0\u1ee3c l\u1ea1i l\u1edbp cha ho\u1eb7c thay \u0111\u1ed5i ho\u00e0n to\u00e0n h\u00e0nh vi c\u1ee7a m\u1ed9t ph\u01b0\u01a1ng th\u1ee9c.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-t\u1eeb-khoa-super\"><strong>T\u1eeb kh\u00f3a super<\/strong><\/h3>\n\n\n\n<p><code>super<\/code> l\u00e0 m\u1ed9t bi\u1ebfn tham chi\u1ebfu \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 tr\u1ecf tr\u1ef1c ti\u1ebfp \u0111\u1ebfn \u0111\u1ed1i t\u01b0\u1ee3ng c\u1ee7a l\u1edbp cha g\u1ea7n nh\u1ea5t. B\u1ea1n s\u1ebd c\u1ea7n \u0111\u1ebfn n\u00f3 trong hai tr\u01b0\u1eddng h\u1ee3p ph\u1ed5 bi\u1ebfn:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>G\u1ecdi Constructor c\u1ee7a l\u1edbp cha:<\/strong> Nh\u01b0 \u0111\u00e3 \u0111\u1ec1 c\u1eadp, Constructor kh\u00f4ng \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba. V\u00ec v\u1eady, ta d\u00f9ng <code>super()<\/code> \u0111\u1ec3 k\u00edch ho\u1ea1t h\u00e0m kh\u1edfi t\u1ea1o c\u1ee7a l\u1edbp cha ngay b\u00ean trong h\u00e0m kh\u1edfi t\u1ea1o c\u1ee7a l\u1edbp con.<\/li>\n\n\n\n<li><strong>Truy c\u1eadp th\u00e0nh ph\u1ea7n b\u1ecb tr\u00f9ng t\u00ean:<\/strong> Khi l\u1edbp con \u0111\u1ecbnh ngh\u0129a m\u1ed9t thu\u1ed9c t\u00ednh ho\u1eb7c ph\u01b0\u01a1ng th\u1ee9c tr\u00f9ng t\u00ean v\u1edbi l\u1edbp cha (\u1ea9n danh), b\u1ea1n c\u00f3 th\u1ec3 d\u00f9ng <code>super.tenPhuongThuc()<\/code> \u0111\u1ec3 ch\u1ec9 \u0111\u1ecbnh r\u00f5 r\u00e0ng r\u1eb1ng b\u1ea1n mu\u1ed1n g\u1ecdi phi\u00ean b\u1ea3n c\u1ee7a l\u1edbp cha.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-ghi-de-ph\u01b0\u01a1ng-th\u1ee9c-method-overriding\"><strong>Ghi \u0111\u00e8 ph\u01b0\u01a1ng th\u1ee9c (Method Overriding)<\/strong><\/h3>\n\n\n\n<p>Ghi \u0111\u00e8 ph\u01b0\u01a1ng th\u1ee9c x\u1ea3y ra khi l\u1edbp con \u0111\u1ecbnh ngh\u0129a l\u1ea1i m\u1ed9t ph\u01b0\u01a1ng th\u1ee9c \u0111\u00e3 t\u1ed3n t\u1ea1i \u1edf l\u1edbp cha \u0111\u1ec3 ph\u00f9 h\u1ee3p v\u1edbi \u0111\u1eb7c th\u00f9 ri\u00eang c\u1ee7a n\u00f3. \u0110\u00e2y ch\u00ednh l\u00e0 c\u00e1ch Java th\u1ef1c hi\u1ec7n t\u00ednh \u0111a h\u00ecnh t\u1ea1i th\u1eddi \u0111i\u1ec3m th\u1ef1c thi (Runtime Polymorphism).<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-quy-t\u1eafc-va-annotation-override\"><strong>Quy t\u1eafc v\u00e0 Annotation @Override<\/strong><\/h3>\n\n\n\n<p>\u0110\u1ec3 ghi \u0111\u00e8 th\u00e0nh c\u00f4ng, ph\u01b0\u01a1ng th\u1ee9c \u1edf l\u1edbp con ph\u1ea3i c\u00f3 c\u00f9ng t\u00ean, c\u00f9ng tham s\u1ed1 v\u00e0 c\u00f9ng ki\u1ec3u tr\u1ea3 v\u1ec1 v\u1edbi ph\u01b0\u01a1ng th\u1ee9c \u1edf l\u1edbp cha.<\/p>\n\n\n\n<p>S\u1eed d\u1ee5ng Annotation <code>@Override<\/code> tr\u01b0\u1edbc ph\u01b0\u01a1ng th\u1ee9c \u1edf l\u1edbp con l\u00e0 m\u1ed9t quy chu\u1ea9n quan tr\u1ecdng:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Gi\u00fap tr\u00ecnh bi\u00ean d\u1ecbch ki\u1ec3m tra l\u1ed7i: N\u1ebfu b\u1ea1n vi\u1ebft sai t\u00ean ph\u01b0\u01a1ng th\u1ee9c ho\u1eb7c tham s\u1ed1, Java s\u1ebd b\u00e1o l\u1ed7i ngay l\u1eadp t\u1ee9c.<\/li>\n\n\n\n<li>T\u0103ng t\u00ednh d\u1ec5 \u0111\u1ecdc: Gi\u00fap c\u1ed9ng s\u1ef1 hi\u1ec3u r\u00f5 \u0111\u00e2y l\u00e0 h\u00e0nh vi \u0111\u01b0\u1ee3c t\u00f9y ch\u1ec9nh l\u1ea1i t\u1eeb l\u1edbp cha.<\/li>\n<\/ul>\n\n\n\n<p>V\u00ed d\u1ee5 minh h\u1ecda:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>class Animal {\n    void makeSound() {\n        System.out.println(\"\u0110\u1ed9ng v\u1eadt ph\u00e1t ra ti\u1ebfng k\u00eau\");\n    }\n}\n\nclass Cat extends Animal {\n    @Override\n    void makeSound() {\n        \/\/ G\u1ecdi ph\u01b0\u01a1ng th\u1ee9c c\u1ee7a l\u1edbp cha n\u1ebfu c\u1ea7n\n        super.makeSound(); \n        \/\/ Sau \u0111\u00f3 th\u1ef1c hi\u1ec7n h\u00e0nh vi ri\u00eang\n        System.out.println(\"Meo meo!\");\n    }\n}<\/code><\/pre>\n\n\n\n<p>Trong v\u00ed d\u1ee5 n\u00e0y, l\u1edbp <code>Cat<\/code> \u0111\u00e3 t\u00f9y bi\u1ebfn l\u1ea1i ph\u01b0\u01a1ng th\u1ee9c <code>makeSound()<\/code>. Khi b\u1ea1n g\u1ecdi ph\u01b0\u01a1ng th\u1ee9c n\u00e0y t\u1eeb m\u1ed9t \u0111\u1ed1i t\u01b0\u1ee3ng <code>Cat<\/code>, ch\u01b0\u01a1ng tr\u00ecnh s\u1ebd \u01b0u ti\u00ean th\u1ef1c hi\u1ec7n logic &#8220;Meo meo&#8221; thay v\u00ec logic chung chung c\u1ee7a l\u1edbp <code>Animal<\/code>.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"581\" height=\"400\" src=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-2.png\" alt=\"\" class=\"wp-image-93924\" srcset=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-2.png 581w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-2-300x207.png 300w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2025\/12\/image-2-200x138.png 200w\" sizes=\"auto, (max-width: 581px) 100vw, 581px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-nh\u1eefng-thanh-ph\u1ea7n-khong-d\u01b0\u1ee3c-k\u1ebf-th\u1eeba-trong-java\"><span class=\"ez-toc-section\" id=\"Nhung_thanh_phan_khong_duoc_ke_thua_trong_Java\"><\/span><strong>Nh\u1eefng th\u00e0nh ph\u1ea7n kh\u00f4ng \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba trong Java<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>M\u1eb7c d\u00f9 k\u1ebf th\u1eeba cho ph\u00e9p l\u1edbp con s\u1edf h\u1eefu c\u00e1c \u0111\u1eb7c t\u00ednh c\u1ee7a l\u1edbp cha, nh\u01b0ng kh\u00f4ng ph\u1ea3i m\u1ecdi th\u1ee9 \u0111\u1ec1u \u0111\u01b0\u1ee3c &#8220;chuy\u1ec3n giao&#8221;. Java \u0111\u1eb7t ra nh\u1eefng gi\u1edbi h\u1ea1n nghi\u00eam ng\u1eb7t \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o t\u00ednh \u0111\u00f3ng g\u00f3i v\u00e0 an to\u00e0n h\u1ec7 th\u1ed1ng:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Private:<\/strong> C\u00e1c thu\u1ed9c t\u00ednh v\u00e0 ph\u01b0\u01a1ng th\u1ee9c \u0111\u01b0\u1ee3c \u0111\u00e1nh d\u1ea5u l\u00e0 <code>private<\/code> th\u00ec kh\u00f4ng th\u1ec3 \u0111\u01b0\u1ee3c truy c\u1eadp tr\u1ef1c ti\u1ebfp t\u1eeb l\u1edbp con. Ch\u00fang \u0111\u01b0\u1ee3c coi l\u00e0 t\u00e0i s\u1ea3n ri\u00eang c\u1ee7a l\u1edbp cha. Tuy nhi\u00ean, l\u1edbp con v\u1eabn c\u00f3 th\u1ec3 t\u01b0\u01a1ng t\u00e1c v\u1edbi c\u00e1c d\u1eef li\u1ec7u n\u00e0y gi\u00e1n ti\u1ebfp th\u00f4ng qua c\u00e1c ph\u01b0\u01a1ng th\u1ee9c <code>public<\/code> ho\u1eb7c <code>protected<\/code> (nh\u01b0 Getter\/Setter) c\u1ee7a l\u1edbp cha.<\/li>\n\n\n\n<li><strong>H\u00e0m kh\u1edfi t\u1ea1o (Constructors):<\/strong> Nh\u01b0 \u0111\u00e3 \u0111\u1ec1 c\u1eadp, l\u1edbp con kh\u00f4ng k\u1ebf th\u1eeba Constructor c\u1ee7a l\u1edbp cha. M\u1ed7i l\u1edbp c\u00f3 nhi\u1ec7m v\u1ee5 t\u1ef1 kh\u1edfi t\u1ea1o tr\u1ea1ng th\u00e1i cho ch\u00ednh m\u00ecnh. Tuy nhi\u00ean, l\u1edbp con b\u1eaft bu\u1ed9c ph\u1ea3i g\u1ecdi Constructor c\u1ee7a l\u1edbp cha (th\u00f4ng qua <code>super()<\/code>) \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o c\u00e1c th\u00e0nh ph\u1ea7n chung \u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp \u0111\u00fang c\u00e1ch tr\u01b0\u1edbc khi th\u1ef1c hi\u1ec7n logic ri\u00eang.<\/li>\n\n\n\n<li><strong>L\u1edbp Final (Final class):<\/strong> Khi m\u1ed9t l\u1edbp \u0111\u01b0\u1ee3c khai b\u00e1o v\u1edbi t\u1eeb kh\u00f3a <code>final<\/code>, n\u00f3 \u0111\u01b0\u1ee3c coi l\u00e0 m\u1ed9t &#8220;\u0111i\u1ec3m d\u1eebng&#8221; trong h\u1ec7 th\u1ed1ng ph\u00e2n c\u1ea5p. C\u00e1c l\u1edbp kh\u00e1c kh\u00f4ng th\u1ec3 k\u1ebf th\u1eeba t\u1eeb m\u1ed9t l\u1edbp <code>final<\/code>. \u0110\u00e2y l\u00e0 c\u00e1ch Java b\u1ea3o v\u1ec7 c\u00e1c l\u1edbp quan tr\u1ecdng (nh\u01b0 l\u1edbp <code>String<\/code>) kh\u00f4ng b\u1ecb thay \u0111\u1ed5i h\u00e0nh vi g\u1ed1c.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-khi-nao-nen-dung-k\u1ebf-th\u1eeba\"><span class=\"ez-toc-section\" id=\"Khi_nao_nen_dung_ke_thua\"><\/span><strong>Khi n\u00e0o n\u00ean d\u00f9ng k\u1ebf th\u1eeba?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>K\u1ebf th\u1eeba r\u1ea5t m\u1ea1nh m\u1ebd nh\u01b0ng n\u1ebfu d\u00f9ng sai c\u00e1ch, n\u00f3 s\u1ebd bi\u1ebfn h\u1ec7 th\u1ed1ng c\u1ee7a b\u1ea1n th\u00e0nh m\u1ed9t m\u1edb h\u1ed7n \u0111\u1ed9n kh\u00f3 b\u1ea3o tr\u00ec. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 nh\u1eefng nguy\u00ean t\u1eafc v\u00e0ng \u0111\u1ec3 quy\u1ebft \u0111\u1ecbnh c\u00f3 n\u00ean s\u1eed d\u1ee5ng k\u1ebf th\u1eeba hay kh\u00f4ng:<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-ch\u1ec9-dung-khi-quan-h\u1ec7-th\u1ef1c-s\u1ef1-la-is-a\"><strong>Ch\u1ec9 d\u00f9ng khi quan h\u1ec7 th\u1ef1c s\u1ef1 l\u00e0 &#8220;IS-A&#8221;<\/strong><\/h3>\n\n\n\n<p>Tr\u01b0\u1edbc khi vi\u1ebft t\u1eeb kh\u00f3a <code>extends<\/code>, h\u00e3y t\u1ef1 \u0111\u1eb7t c\u00e2u h\u1ecfi: &#8220;L\u1edbp con c\u00f3 th\u1ef1c s\u1ef1 l\u00e0 m\u1ed9t phi\u00ean b\u1ea3n \u0111\u1eb7c bi\u1ec7t c\u1ee7a l\u1edbp cha kh\u00f4ng?&#8221;.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u0110\u00fang: <code>Samsung<\/code> IS-A <code>Smartphone<\/code>.<\/li>\n\n\n\n<li>Sai: <code>Engine<\/code> IS-A <code>Car<\/code> (\u0110\u1ed9ng c\u01a1 kh\u00f4ng ph\u1ea3i l\u00e0 m\u1ed9t chi\u1ebfc xe h\u01a1i, n\u00f3 ch\u1ec9 l\u00e0 m\u1ed9t b\u1ed9 ph\u1eadn c\u1ee7a xe).<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-tranh-l\u1ea1m-d\u1ee5ng-k\u1ebf-th\u1eeba-qua-sau-deep-hierarchies\"><strong>Tr\u00e1nh l\u1ea1m d\u1ee5ng k\u1ebf th\u1eeba qu\u00e1 s\u00e2u (Deep Hierarchies)<\/strong><\/h3>\n\n\n\n<p>Vi\u1ec7c t\u1ea1o ra m\u1ed9t c\u00e2y k\u1ebf th\u1eeba qu\u00e1 nhi\u1ec1u t\u1ea7ng (v\u00ed d\u1ee5: L\u1edbp A -&gt; B -&gt; C -&gt; D -&gt; E) s\u1ebd g\u00e2y ra t\u00ecnh tr\u1ea1ng &#8220;gi\u00f2n&#8221; m\u00e3 ngu\u1ed3n. M\u1ed9t thay \u0111\u1ed5i nh\u1ecf \u1edf l\u1edbp A c\u00f3 th\u1ec3 l\u00e0m h\u1ecfng logic c\u1ee7a t\u1ea5t c\u1ea3 c\u00e1c l\u1edbp con ph\u00eda d\u01b0\u1edbi. Quy t\u1eafc ng\u1ea7m trong thi\u1ebft k\u1ebf h\u1ec7 th\u1ed1ng l\u00e0 gi\u1eef cho c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p c\u00e0ng n\u00f4ng c\u00e0ng t\u1ed1t \u0111\u1ec3 d\u1ec5 ki\u1ec3m so\u00e1t v\u00e0 g\u1ee1 l\u1ed7i.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-phan-bi\u1ec7t-k\u1ebf-th\u1eeba-inheritance-va-t\u1ed5ng-h\u1ee3p-composition\"><strong>Ph\u00e2n bi\u1ec7t K\u1ebf th\u1eeba (Inheritance) v\u00e0 T\u1ed5ng h\u1ee3p (Composition)<\/strong><\/h3>\n\n\n\n<p>Trong l\u1eadp tr\u00ecnh, c\u00f3 m\u1ed9t c\u00e2u ch\u00e2m ng\u00f4n n\u1ed5i ti\u1ebfng: <em>&#8220;\u01afu ti\u00ean t\u1ed5ng h\u1ee3p h\u01a1n k\u1ebf th\u1eeba&#8221;<\/em> (Favor composition over inheritance).<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>K\u1ebf th\u1eeba (Inheritance):<\/strong> Thi\u1ebft l\u1eadp m\u1ed1i quan h\u1ec7 <strong>&#8220;IS-A&#8221;<\/strong> (L\u00e0 m\u1ed9t). D\u00f9ng khi b\u1ea1n mu\u1ed1n chia s\u1ebb h\u00e0nh vi chung v\u00e0 t\u1eadn d\u1ee5ng t\u00ednh \u0111a h\u00ecnh.<\/li>\n\n\n\n<li><strong>T\u1ed5ng h\u1ee3p (Composition):<\/strong> Thi\u1ebft l\u1eadp m\u1ed1i quan h\u1ec7 <strong>&#8220;HAS-A&#8221;<\/strong> (C\u00f3 m\u1ed9t). Thay v\u00ec k\u1ebf th\u1eeba, b\u1ea1n khai b\u00e1o m\u1ed9t \u0111\u1ed1i t\u01b0\u1ee3ng c\u1ee7a l\u1edbp kh\u00e1c l\u00e0m thu\u1ed9c t\u00ednh b\u00ean trong l\u1edbp c\u1ee7a m\u00ecnh.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-khi-nao-nen-ch\u1ecdn-inheritance-hay-composition\"><strong>Khi n\u00e0o n\u00ean ch\u1ecdn Inheritance hay Composition?<\/strong><\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>T\u00ecnh hu\u1ed1ng<\/strong><\/td><td><strong>L\u1ef1a ch\u1ecdn t\u1ed1i \u01b0u<\/strong><\/td><\/tr><tr><td>Khi \u0111\u1ed1i t\u01b0\u1ee3ng A l\u00e0 m\u1ed9t lo\u1ea1i c\u1ee5 th\u1ec3 c\u1ee7a \u0111\u1ed1i t\u01b0\u1ee3ng B.<\/td><td>Inheritance<\/td><\/tr><tr><td>Khi \u0111\u1ed1i t\u01b0\u1ee3ng A \u0111\u01b0\u1ee3c c\u1ea5u t\u1ea1o t\u1eeb \u0111\u1ed1i t\u01b0\u1ee3ng B.<\/td><td>Composition<\/td><\/tr><tr><td>Khi b\u1ea1n mu\u1ed1n thay \u0111\u1ed5i h\u00e0nh vi c\u1ee7a \u0111\u1ed1i t\u01b0\u1ee3ng linh ho\u1ea1t ngay l\u00fac ch\u01b0\u01a1ng tr\u00ecnh \u0111ang ch\u1ea1y.<\/td><td>Composition<\/td><\/tr><tr><td>Khi b\u1ea1n mu\u1ed1n l\u1edbp con t\u1ef1 \u0111\u1ed9ng c\u00f3 t\u1ea5t c\u1ea3 c\u00e1c t\u00ednh n\u0103ng c\u1ee7a l\u1edbp cha m\u00e0 kh\u00f4ng c\u1ea7n vi\u1ebft l\u1ea1i.<\/td><td>Inheritance<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p><strong>V\u00ed d\u1ee5:<\/strong> M\u1ed9t chi\u1ebfc <code>Car<\/code> kh\u00f4ng n\u00ean k\u1ebf th\u1eeba t\u1eeb <code>Engine<\/code>. Thay v\u00e0o \u0111\u00f3, <code>Car<\/code> n\u00ean c\u00f3 m\u1ed9t bi\u1ebfn thu\u1ed9c t\u00ednh l\u00e0 <code>Engine<\/code> (Composition). \u0110i\u1ec1u n\u00e0y gi\u00fap b\u1ea1n d\u1ec5 d\u00e0ng thay \u0111\u1ed5i c\u00e1c lo\u1ea1i \u0111\u1ed9ng c\u01a1 kh\u00e1c nhau cho xe m\u00e0 kh\u00f4ng c\u1ea7n thay \u0111\u1ed5i c\u1ea5u tr\u00fac l\u1edbp.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-cac-cau-h\u1ecfi-th\u01b0\u1eddng-g\u1eb7p-v\u1ec1-k\u1ebf-th\u1eeba-trong-java\"><span class=\"ez-toc-section\" id=\"Cac_cau_hoi_thuong_gap_ve_ke_thua_trong_Java\"><\/span><strong>C\u00e1c c\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p v\u1ec1 k\u1ebf th\u1eeba trong Java<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-m\u1ed9t-l\u1edbp-co-th\u1ec3-k\u1ebf-th\u1eeba-t\u1eeb-nhi\u1ec1u-l\u1edbp-cha-cung-luc-khong\"><strong>M\u1ed9t l\u1edbp c\u00f3 th\u1ec3 k\u1ebf th\u1eeba t\u1eeb nhi\u1ec1u l\u1edbp cha c\u00f9ng l\u00fac kh\u00f4ng?<\/strong><\/h3>\n\n\n\n<p><strong>Kh\u00f4ng.<\/strong> Trong Java, m\u1ed9t l\u1edbp ch\u1ec9 c\u00f3 th\u1ec3 k\u1ebf th\u1eeba t\u1eeb duy nh\u1ea5t m\u1ed9t l\u1edbp cha (Single Inheritance). \u0110i\u1ec1u n\u00e0y gi\u00fap tr\u00e1nh xung \u0111\u1ed9t v\u00e0 nh\u1ea7m l\u1eabn khi c\u00e1c l\u1edbp cha c\u00f3 c\u00e1c ph\u01b0\u01a1ng th\u1ee9c tr\u00f9ng t\u00ean nhau (V\u1ea5n \u0111\u1ec1 &#8220;Kim c\u01b0\u01a1ng&#8221;). \u0110\u1ec3 \u0111\u1ea1t \u0111\u01b0\u1ee3c hi\u1ec7u qu\u1ea3 t\u01b0\u01a1ng t\u1ef1 \u0111a k\u1ebf th\u1eeba, b\u1ea1n n\u00ean s\u1eed d\u1ee5ng <strong>Interface<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-t\u1ea1i-sao-toi-nen-dung-override-khi-ghi-de-ph\u01b0\u01a1ng-th\u1ee9c\"><strong>T\u1ea1i sao t\u00f4i n\u00ean d\u00f9ng <\/strong><strong>@Override<\/strong><strong> khi ghi \u0111\u00e8 ph\u01b0\u01a1ng th\u1ee9c?<\/strong><\/h3>\n\n\n\n<p>M\u1eb7c d\u00f9 kh\u00f4ng b\u1eaft bu\u1ed9c v\u1ec1 m\u1eb7t c\u00fa ph\u00e1p, nh\u01b0ng <code>@Override<\/code> gi\u00fap tr\u00ecnh bi\u00ean d\u1ecbch ki\u1ec3m tra xem b\u1ea1n c\u00f3 th\u1ef1c s\u1ef1 \u0111ang ghi \u0111\u00e8 m\u1ed9t ph\u01b0\u01a1ng th\u1ee9c t\u1eeb l\u1edbp cha hay kh\u00f4ng. N\u1ebfu b\u1ea1n vi\u1ebft sai t\u00ean ph\u01b0\u01a1ng th\u1ee9c (v\u00ed d\u1ee5: <code>makeSounds()<\/code> thay v\u00ec <code>makeSound()<\/code>), tr\u00ecnh bi\u00ean d\u1ecbch s\u1ebd b\u00e1o l\u1ed7i ngay l\u1eadp t\u1ee9c thay v\u00ec t\u1ea1o ra m\u1ed9t ph\u01b0\u01a1ng th\u1ee9c m\u1edbi ho\u00e0n to\u00e0n.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-s\u1ef1-khac-bi\u1ec7t-gi\u1eefa-this-va-super-la-gi\"><strong>S\u1ef1 kh\u00e1c bi\u1ec7t gi\u1eefa <\/strong><strong>this<\/strong><strong> v\u00e0 <\/strong><strong>super<\/strong><strong> l\u00e0 g\u00ec?<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>this<\/strong><strong>:<\/strong> Tham chi\u1ebfu \u0111\u1ebfn \u0111\u1ed1i t\u01b0\u1ee3ng hi\u1ec7n t\u1ea1i c\u1ee7a l\u1edbp \u0111\u00f3.<\/li>\n\n\n\n<li><strong>super<\/strong><strong>:<\/strong> Tham chi\u1ebfu \u0111\u1ebfn \u0111\u1ed1i t\u01b0\u1ee3ng c\u1ee7a l\u1edbp cha g\u1ea7n nh\u1ea5t. C\u1ea3 hai \u0111\u1ec1u th\u01b0\u1eddng \u0111\u01b0\u1ee3c d\u00f9ng \u0111\u1ec3 ph\u00e2n bi\u1ec7t khi t\u00ean thu\u1ed9c t\u00ednh ho\u1eb7c ph\u01b0\u01a1ng th\u1ee9c \u1edf l\u1edbp con b\u1ecb tr\u00f9ng v\u1edbi l\u1edbp cha ho\u1eb7c tham s\u1ed1 truy\u1ec1n v\u00e0o.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-co-cach-nao-ngan-m\u1ed9t-ph\u01b0\u01a1ng-th\u1ee9c-khong-b\u1ecb-ghi-de-\u1edf-l\u1edbp-con-khong\"><strong>C\u00f3 c\u00e1ch n\u00e0o ng\u0103n m\u1ed9t ph\u01b0\u01a1ng th\u1ee9c kh\u00f4ng b\u1ecb ghi \u0111\u00e8 \u1edf l\u1edbp con kh\u00f4ng?<\/strong><\/h3>\n\n\n\n<p><strong>C\u00f3.<\/strong> B\u1ea1n h\u00e3y th\u00eam t\u1eeb kh\u00f3a final v\u00e0o tr\u01b0\u1edbc ph\u01b0\u01a1ng th\u1ee9c \u1edf l\u1edbp cha. V\u00ed d\u1ee5: <code>public final void show()<\/code>. Khi \u0111\u00f3, c\u00e1c l\u1edbp con k\u1ebf th\u1eeba t\u1eeb l\u1edbp n\u00e0y s\u1ebd kh\u00f4ng th\u1ec3 \u0111\u1ecbnh ngh\u0129a l\u1ea1i ph\u01b0\u01a1ng th\u1ee9c <code>show()<\/code> \u0111\u01b0\u1ee3c n\u1eefa.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"h-private-member-co-th\u1ef1c-s\u1ef1-d\u01b0\u1ee3c-k\u1ebf-th\u1eeba-khong\"><strong>Private member c\u00f3 th\u1ef1c s\u1ef1 \u0111\u01b0\u1ee3c k\u1ebf th\u1eeba kh\u00f4ng?<\/strong><\/h3>\n\n\n\n<p>V\u1ec1 m\u1eb7t l\u00fd thuy\u1ebft, l\u1edbp con v\u1eabn ch\u1ee9a c\u00e1c th\u00e0nh ph\u1ea7n <code>private<\/code> c\u1ee7a l\u1edbp cha nh\u01b0ng n\u00f3 <strong>kh\u00f4ng c\u00f3 quy\u1ec1n truy c\u1eadp tr\u1ef1c ti\u1ebfp<\/strong>. \u0110\u1ec3 thao t\u00e1c v\u1edbi c\u00e1c th\u00e0nh ph\u1ea7n n\u00e0y, b\u1ea1n ph\u1ea3i th\u00f4ng qua c\u00e1c ph\u01b0\u01a1ng th\u1ee9c h\u1ed7 tr\u1ee3 (nh\u01b0 Getter\/Setter) ho\u1eb7c \u0111\u1ed5i quy\u1ec1n truy c\u1eadp sang <code>protected<\/code>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-k\u1ebft-lu\u1eadn\"><span class=\"ez-toc-section\" id=\"Ket_luan\"><\/span><strong>K\u1ebft lu\u1eadn<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>K\u1ebf th\u1eeba trong Java l\u00e0 m\u1ed9t trong b\u1ed1n tr\u1ee5 c\u1ed9t quan tr\u1ecdng nh\u1ea5t c\u1ee7a l\u1eadp tr\u00ecnh h\u01b0\u1edbng \u0111\u1ed1i t\u01b0\u1ee3ng trong Java. Hy v\u1ecdng qua b\u00e0i vi\u1ebft n\u00e0y, b\u1ea1n \u0111\u00e3 n\u1eafm v\u1eefng c\u00e1ch s\u1eed d\u1ee5ng t\u1eeb kh\u00f3a <code>extends<\/code>, hi\u1ec3u \u0111\u01b0\u1ee3c t\u1ea7m quan tr\u1ecdng c\u1ee7a <code>super<\/code> v\u00e0 bi\u1ebft c\u00e1ch thi\u1ebft k\u1ebf h\u1ec7 th\u1ed1ng sao cho linh ho\u1ea1t, tr\u00e1nh \u0111\u01b0\u1ee3c nh\u1eefng sai l\u1ea7m ph\u1ed5 bi\u1ebfn.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>K\u1ebf th\u1eeba (Inheritance) trong Java l\u00e0 c\u01a1 ch\u1ebf cho ph\u00e9p m\u1ed9t l\u1edbp con s\u1edf h\u1eefu l\u1ea1i to\u00e0n b\u1ed9 c\u00e1c thu\u1ed9c t\u00ednh v\u00e0 ph\u01b0\u01a1ng th\u1ee9c t\u1eeb l\u1edbp cha, gi\u00fap t\u1ed1i \u01b0u h\u00f3a vi\u1ec7c t\u00e1i s\u1eed d\u1ee5ng m\u00e3 ngu\u1ed3n (Reusability). Vi\u1ec7c \u00e1p d\u1ee5ng k\u1ebf th\u1eeba c\u1ea7n s\u1ef1 t\u00ednh to\u00e1n k\u1ef9 l\u01b0\u1ee1ng \u0111\u1ec3 tr\u00e1nh t\u1ea1o ra c\u1ea5u tr\u00fac [&hellip;]<\/p>\n","protected":false},"author":203,"featured_media":95520,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_gspb_post_css":"","footnotes":""},"categories":[109,10350],"tags":[],"class_list":["post-93922","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-chuyen-mon-it","category-java"],"blocksy_meta":[],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v26.8 (Yoast SEO v27.7) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>K\u1ebf th\u1eeba trong Java: Kh\u00e1i ni\u1ec7m, ph\u00e2n lo\u1ea1i v\u00e0 nh\u1eefng l\u01b0u \u00fd - ITviec Blog<\/title>\n<meta name=\"description\" content=\"Chi ti\u1ebft k\u1ebf th\u1eeba trong Java k\u00e8m v\u00ed d\u1ee5: c\u00e1c lo\u1ea1i k\u1ebf th\u1eeba, t\u1eeb kh\u00f3a quan tr\u1ecdng, khi n\u00e0o n\u00ean d\u00f9ng v\u00e0 kh\u00f4ng n\u00ean d\u00f9ng k\u1ebf th\u1eeba trong Java.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"K\u1ebf th\u1eeba trong Java: Kh\u00e1i ni\u1ec7m, ph\u00e2n lo\u1ea1i v\u00e0 nh\u1eefng l\u01b0u \u00fd\" \/>\n<meta property=\"og:description\" content=\"K\u1ebf th\u1eeba (Inheritance) trong Java l\u00e0 c\u01a1 ch\u1ebf cho ph\u00e9p m\u1ed9t l\u1edbp con s\u1edf h\u1eefu l\u1ea1i to\u00e0n b\u1ed9 c\u00e1c thu\u1ed9c t\u00ednh v\u00e0 ph\u01b0\u01a1ng th\u1ee9c t\u1eeb l\u1edbp cha, gi\u00fap t\u1ed1i \u01b0u h\u00f3a vi\u1ec7c t\u00e1i s\u1eed\" \/>\n<meta property=\"og:url\" content=\"https:\/\/itviec.com\/blog\/ke-thua-trong-java\/\" \/>\n<meta property=\"og:site_name\" content=\"ITviec Blog\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/ITviec\" \/>\n<meta property=\"article:published_time\" content=\"2026-04-12T12:05:14+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-04-12T13:57:07+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2026\/04\/ke-thua-trong-java-scaled.png\" \/>\n\t<meta property=\"og:image:width\" content=\"800\" \/>\n\t<meta property=\"og:image:height\" content=\"421\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"Tien Tran\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@ITviec\" \/>\n<meta name=\"twitter:site\" content=\"@ITviec\" \/>\n<meta name=\"twitter:label1\" content=\"\u0110\u01b0\u1ee3c vi\u1ebft b\u1edfi\" \/>\n\t<meta name=\"twitter:data1\" content=\"Tien Tran\" \/>\n\t<meta name=\"twitter:label2\" content=\"\u01af\u1edbc t\u00ednh th\u1eddi gian \u0111\u1ecdc\" \/>\n\t<meta name=\"twitter:data2\" content=\"13 ph\u00fat\" \/>\n<!-- \/ Yoast SEO Premium plugin. -->","yoast_head_json":{"title":"K\u1ebf th\u1eeba trong Java: Kh\u00e1i ni\u1ec7m, ph\u00e2n lo\u1ea1i v\u00e0 nh\u1eefng l\u01b0u \u00fd - 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