在Java中是否可以基于构造函数调用初始化最终数据成员？

Question

是否可以按照下面的类中的指定进行修改,并将现有调用者的成员初始化为某个默认值,比如说null？

成员必须是私人决赛作为持久性要求.

// initial version of the class
public class A {
    A() {
        // do some work here
    }
}

// the following modification required adding additional constructor to the class with **member** data member.
public class A {
    private final String member;

    A(String member) {
        this();
        this.member = member;   
    }

    A() {
        // initilize member to null if a client called this constructor
        // do some work here
    }
}

Answer 1

为什么你不能拥有:

public class A {
    private final String member;

    A(String member) {
        this.member = member;   
    }

    A() {
        this(null);
    }
}

这是构造函数链接的常用模式; 具有较少特定版本的版本调用更具体的版本,并根据需要提供默认参数.

Answer 2

是!

public class A {
    private final String member;

    A(String member) {
        this.member = member;
        // do some work here instead   
    }

    A() {
        this(null);
    }
}