在Java中是否可以基于构造函数调用来初始化最终数据成员？ [英] Is it possible in Java to initialise a final data member based on constructor call?

问题描述

可以按照下面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，例如 null

Is it possible to make a modification as specified in the class below, and initialize a member for existing callers to some default value, say null?

会员必须以私人最终作为持续性要求。

Member is required to be private final as persistence requirement.

// 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
    }
}

推荐答案

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通常模式;让较不具体的版本调用更具体的版本，根据需要提供默认参数。

This is the usual pattern for constructor chaining; have the less-specific versions call the more-specific versions, supplying default parameters as appropriate.

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