Java 不可变对象

如果一个对象的状态在构造后不能改变，则该对象被认为是不可变的。例如 String。

不可变对象在并发应用程序中特别有用。由于它们不能改变状态，因此它们不会被线程干扰破坏或在不一致状态下被观察到。

 

定义一个普通同步类（可变对象）

package com.example.Immutable;

public class SynchronizedRGB {

    // 值必须介于0到255之间
    private int red;
    private int green;
    private int blue;
    private String name;

    private void check(int red, int green, int blue) {
        if (red < 0 || red > 255 || green < 0 || green > 255 || blue < 0 || blue > 255) {
            throw new IllegalArgumentException();
        }
    }

    public SynchronizedRGB(int red, int green, int blue, String name) {
        check(red, green, blue);
        this.red = red;
        this.green = green;
        this.blue = blue;
        this.name = name;
    }

    public void set(int red, int green, int blue, String name) {
        check(red, green, blue);
        synchronized (this) {
            this.red = red;
            this.green = green;
            this.blue = blue;
            this.name = name;
        }
    }

    public synchronized int getRGB() {
        return ((red << 16) | (green << 8) | blue);
    }

    public synchronized String getName() {
        return name;
    }

    public synchronized void invert() {
        red = 255 - red;
        green = 255 - green;
        blue = 255 - blue;
        name = "Inverse of " + name;
    }
}

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