Java继承——代码块与构造器

示例

class Parent {
    static {
        System.out.println("Parent's static code block...");
    }

    {
        System.out.println("Parent's constructor code block...");
    }

    public Parent() {
        System.out.println("Parent's constructor without arguments...");
    }

}

class Children extends Parent {
    private String name;

    static {
        System.out.println("Children's static code block...");
    }

    {
        System.out.println("Children's constructor code block...");
    }

    public Children() {
        System.out.println("Children's constructor without arguments...");
    }

    public Children(String name) {
        this.name = name;
        System.out.println("Children's constructor with arguments...");
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

public class ExtendTest {

    public static void main(String[] args) {
        /* * ExtendTest's static code block is executed... * Parent's static code block... * Parent's constructor code block... * Parent's constructor without arguments... * ------------------------ * Parent's constructor code block... * Parent's constructor without arguments... */
        /*Parent p1 = new Parent(); System.out.println("------------------------"); Parent p2 = new Parent();*/

        /* * ExtendTest's static code block is executed... * Parent's static code block... * Children's static code block... * Parent's constructor code block... * Parent's constructor without arguments... * Children's constructor code block... * Children's constructor without arguments... * ------------------------ * Parent's constructor code block... * Parent's constructor without arguments... * Children's constructor code block... * Children's constructor with arguments... */
        Children c1 = new Children();
        System.out.println("------------------------");
        Children c2 = new Children("Bob");
    }

    static {
        System.out.println("ExtendTest's static code block is executed...");
    }
}

总结

静态代码块：
1. 静态代码块只能在类中由static{}进行声明创建，不能放在类中的方法中或其他代码块中
2. 静态代码块属于类，在类被JVM加载时被执行，只会执行一次
3. 静态代码块先于main()方法执行
4. 静态代码块用于给类初始化
构造代码块
1. 构造代码块只能在类中由{}进行声明创建，若放在类中的方法中或其他代码块中，则称之为“局部代码块”
2. 构造代码块会在创建对象时，先于构造器执行
3. 构造代码块用于给对象进行统一初始化