Java 初始化顺序

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初始化操作的执行顺序：

  1. 所有静态成员/初始块先执行
  2. 父类初始化完成（非静态成员/初始块执行 -> 构造函数调用）
  3. 子类初始化完成（非静态成员/初始块执行 -> 构造函数调用）

例子：

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/**
 * 父类
 */
public class Parent {
    static int a1 = intA1();
    static int intA1(){
        System.out.println("1. Parent, static int a1 = intA1();");
        return 0;
    }
    {
        System.out.println("6. Parent, non-static initial block1");
    }
    static {
        System.out.println("2. Parent, static initial block1");
    }
    {
        System.out.println("7. Parent, non-static initial block2");
    }
    static {
        System.out.println("3. Parent, static initial block2");
    }
    static int a2 = intA2();
    static int intA2(){
        System.out.println("4. Parent, static int a2 = intA2();");
        return 0;
    }
    public Parent() {
        System.out.println("8. Parent, constructor method");
    }
}
/**
 * 子类
 */
public class Child extends Parent{
    {
        System.out.println("9. Child, non-static initial block1");
    }
    int c1 = intC1();
    int intC1(){
        System.out.println("10. Child, int c1 = intC1();");
        return 0;
    }
    {
        System.out.println("11. Child, non-static initial block2");
    }
    static{
        System.out.println("5. Child, static initial block1");
    }
    public Child() {
        System.out.println("12. Child, constructor method");
    }
}
/**
 * 测试类
 */
public class ExeSeqTest {
    public static void main(String[] args) {
        Child child = new Child();
    }
}

执行顺序结果如下:

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1. Parent, static int a1 = intA1();
2. Parent, static initial block1
3. Parent, nonstatic initial block2
4. Parent, static int a2 = intA2();
5. Child, static initial block1
6. Parent, non-static initial block1
7. Parent, non-static initial block2
8. Parent, constructor method
9. Child, non-static initial block1
10. Child, int c1 = intC1();
11. Child, non-static initial block2
12. Child, constructor method