Java奇怪的位移_Java中位移的疑惑

看来来晚了...

扔个代码闪人了吧

/**

* 如何生成二进制全1的数

* @author Jeky

*/

public class Rotate {

private static final long TIME = 1000000L;

private static final int LENGTH = 10;

public static void main(String[] args) {

test(new Runnable() {

public void run() {

generateHighBits1(LENGTH);

}

});

test(new Runnable() {

public void run() {

generateHighBits2(LENGTH);

}

});

test(new Runnable() {

public void run() {

generateHighBits3(LENGTH);

}

});

test(new Runnable() {

public void run() {

generateHighBits4(LENGTH);

}

});

}

public static void test(Runnable run) {

long start = System.nanoTime();

for (int i = 0; i < TIME; i++) {

run.run();

}

long end = System.nanoTime();

System.out.println(end - start);

}

public static int generateHighBits1(int length) {

return (int) (Math.pow(2, length) - 1);

}

public static int generateHighBits2(int length) {

return -1 >>> -length;

}

public static int generateHighBits3(int length) {

return HIGH_BITS[length];

}

public static int generateHighBits4(int length) {

StringBuilder buf = new StringBuilder();

for (int i = 0; i < length; i++) {

buf.append(1);

}

return Integer.parseInt(buf.toString(), 2);

}

private static final int[] HIGH_BITS = new int[32];

static {

for (int i = 0; i < HIGH_BITS.length; i++) {

HIGH_BITS[i] = generateHighBits1(i);

}

}

}