java - 这条线是什么意思？

Question

我正在查看示例游戏项目。你能解释一下这些行吗:

public static final int GAMEPAD_UP = 0x0040;

0x0040;有什么用？

完整代码:

package com.androidemu;

public class Emulator {
    public static final int VIDEO_W = 240;
    public static final int VIDEO_H = 160;

    public static final int GAMEPAD_UP        = 0x0040;
    public static final int GAMEPAD_DOWN    = 0x0080;
    public static final int GAMEPAD_LEFT    = 0x0020;
    public static final int GAMEPAD_RIGHT    = 0x0010;
    public static final int GAMEPAD_A        = 0x0001;
    public static final int GAMEPAD_B        = 0x0002;
    public static final int GAMEPAD_SELECT    = 0x0004;
    public static final int GAMEPAD_START    = 0x0008;
    public static final int GAMEPAD_TL        = 0x0200;
    public static final int GAMEPAD_TR        = 0x0100;

    public static final int GAMEPAD_A_TURBO    = (GAMEPAD_A << 16);
    public static final int GAMEPAD_B_TURBO    = (GAMEPAD_B << 16);

    public static final int GAMEPAD_UP_LEFT = (GAMEPAD_UP | GAMEPAD_LEFT);
    public static final int GAMEPAD_UP_RIGHT = (GAMEPAD_UP | GAMEPAD_RIGHT);
    public static final int GAMEPAD_DOWN_LEFT = (GAMEPAD_DOWN | GAMEPAD_LEFT);
    public static final int GAMEPAD_DOWN_RIGHT = (GAMEPAD_DOWN | GAMEPAD_RIGHT);

    public native void setRenderSurface(EmulatorView surface,
            int width, int height);
    public native void setKeyStates(int states);
    public native void setOption(String name, String value);

    public native boolean initialize(String libdir, String datadir);
    public native void cleanUp();
    public native void reset();
    public native void power();
    public native boolean loadBIOS(String file);
    public native boolean loadROM(String file);
    public native void unloadROM();
    public native void pause();
    public native void resume();
    public native void run();
    public native boolean saveState(String file);
    public native boolean loadState(String file);

    public void setOption(String name, boolean value) {
        setOption(name, value ? "true" : "false");
    }

    static {
        System.loadLibrary("gba");
    }
}

这些值的用途是什么？

Answer 1

这是一个只有一位设置的值:

00000000000000000000000001000000

所以你也可以有，比方说，GAMEPAD_RIGHT=0x0010，你可以通过 AND'ing 对它们中的任何一个分别进行 OR 值和测试。它在游戏中很常见，尤其是在移动设备上。

这样编码的目的是为了优化空间，并且能够在一行中测试各种情况。

例如，通过对每个可能的游戏 handle 键使用一位，您可以在一个 int 上表示(即使在旧的 8 位控制台时代，控制台只有很少的键，也可以在一个字节上表示)每个键的状态(它是“开”或“关”)。

UP + RIGHT，同时按下两个键，给出:

00000000000000000000000001000000

               OR

00000000000000000000000000010000

               =

00000000000000000000000001010000