Java 中是否可以根据构造函数调用来初始化最终数据成员？

发布于 2024-11-14 00:51:49 字数 612 浏览 1 评论 0原文

是否可以按照下面的类中指定的方式进行修改，并将现有调用者的成员初始化为某个默认值，例如null？

作为持久性要求，成员必须是私有最终。

// 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
    }
}

原文

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?

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
    }
}

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满身野味 2024-11-21 00:51:49

为什么你不能直接拥有：

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见模式；让不太具体版本调用更具体版本，并根据需要提供默认参数。

Why can't you just have:

public class A {
    private final String member;

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

    A() {
        this(null);
    }
}

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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究竟谁懂我的在乎 2024-11-21 00:51:49

是的！

public class A {
    private final String member;

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

    A() {
        this(null);
    }
}

Yes!

public class A {
    private final String member;

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

    A() {
        this(null);
    }
}

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