java - 为什么 getRGB() 方法是这样写的？是否有其他方法来编写 getRGB() 方法？

Question

我是 Java 新手。我从Java教程Oracle中看到了下面的代码。我正在努力理解此代码片段的用途:

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

我理解按位运算符的工作原理，但我很难理解为什么 getRGB() 方法是这样编写的。是否有其他方法来编写 getRGB() 方法？

public class SynchronizedRGB {

    // Values must be between 0 and 255.
    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;
    }

    public static void main(String[] args) {
        SynchronizedRGB color = new SynchronizedRGB(0, 0, 0, "Pitch black");
        System.out.println(color.getRGB());
    }
}

Answer 1

左移运算符<< x相当于乘以2^x，所以可以写成

return ((red * 65536 ) + (green *256) + blue);