无法为最终变量“名称"分配值 [英] Cannot assign a value to final variable 'name'

问题描述

为什么 Java 不允许我间接初始化最终变量?我不明白为什么它不起作用，我的意思是该方法将始终运行，因此，如果直接或通过方法进行初始化，会产生什么不同?

Why isn't Java allowing me to initialize final variables indirectly? I don't see why it shouldn't work, I mean the method will always run so what difference does it make if initialized directly or via method?

此代码有效:

package com.company;

public class Person {

    private final String name;

    public Person() {
        name = "bob";
    }
}

这不是.(即使我摆脱了IO代码并硬编码分配给name的值)

This one doesn't. (even if I get rid of IO code and hardcode the value assigned to name)

package com.company;

import java.util.Scanner;

public class Person {

    private final String name;

    public Person() {
        askName();
    }

    public void askName() {
        Scanner scanner = new Scanner(System.in);
        name = scanner.nextLine();
    }
}

推荐答案

final 字段必须在构造函数中设置.您可以执行以下操作.

final fields must be set in the constructor. What you can do is the following.

import java.util.Scanner;

public class Person {

    private final String name;

    public Person() {
        name = askName();
    }

    public static String askName() {
        Scanner scanner = new Scanner(System.in);
        return scanner.nextLine();
    }
}

但是，更好的选择可能会注入您所需的值.

However, a better option is likely to inject the value you need.

import java.util.Scanner;

public class Person {

    private final String name;

    public Person(String name) {
        this.name = name;
    }

    public static Person askName() {
        Scanner scanner = new Scanner(System.in);
        return new Person(scanner.nextLine());
    }
}

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