{"path":"1923662","ref":"空白final.md","title":"空白 final","content":"### [空白 final](https:\/\/lingcoder.gitee.io\/onjava8\/#\/book\/08-Reuse?id=%e7%a9%ba%e7%99%bd-final)\n\n空白 final 指的是没有初始化值的**final**属性。编译器确保空白 final 在使用前必须被初始化。这样既能使一个类的每个对象的**final**属性值不同，也能保持它的不变性。\n\n~~~\n\/\/ reuse\/BlankFinal.java\n\/\/ \"Blank\" final fields\nclass Poppet {\n    private int i;\n\n    Poppet(int ii) {\n        i = ii;\n    }\n}\n\npublic class BlankFinal {\n    private final int i = 0; \/\/ Initialized final\n    private final int j; \/\/ Blank final\n    private final Poppet p; \/\/ Blank final reference\n    \/\/ Blank finals MUST be initialized in constructor\n    public BlankFinal() {\n        j = 1; \/\/ Initialize blank final\n        p = new Poppet(1); \/\/ Init blank final reference\n    }\n\n    public BlankFinal(int x) {\n        j = x; \/\/ Initialize blank final\n        p = new Poppet(x); \/\/ Init blank final reference\n    }\n\n    public static void main(String[] args) {\n        new BlankFinal();\n        new BlankFinal(47);\n    }\n}\n~~~\n\n你必须在定义时或在每个构造器中执行 final 变量的赋值操作。这保证了 final 属性在使用前已经被初始化过。\n\n"}