Java中自增（++）和赋值（=）运算效率比较

前言

将一个int型数组x[]从初值0变成1。有两种做法：

// 只考虑后自增
int length = x.length;
for (int i = 0; i < length; i++) {
	x[i]++;
}

int length = x.length;
for (int i = 0; i < length; i++) {
	x[i] = 1;
}

测试代码

/**
 * @author PengHao
 * @version 1.0
 * @date 2019-04-30 下午6:38:02
 * Environment: Windows 10
 * IDE Version: Eclipse 2019-3
 * JDK Version: JDK1.8.0_112
 */

public class Efficiency {
	private static int LENGTH = 21474836;
	private static long begin, end;

	/**
	 * @return 自增运算用时
	 */
	private static long autoIncrementAfter() {
		int[] x = new int[LENGTH];
		begin = System.currentTimeMillis(); // 当前时间
		for (int i = 0; i < LENGTH; i++) {
			x[i]++;
		}
		end = System.currentTimeMillis(); // 当前时间
		return end - begin; // 循环用时
	}

	/**
	 * @return 赋值运算用时
	 */
	private static long copyValue() {
		begin = System.currentTimeMillis();
		int[] x = new int[LENGTH];
		for (int i = 0; i < LENGTH; i++) {
			x[i] = 1;
		}
		end = System.currentTimeMillis();
		return end - begin;
	}

	public static void main(String[] args) {
		System.out.println("LENGTH=" + LENGTH);
		System.out.println("后自增用时：" + autoIncrementAfter());
		System.out.println("赋值用时：" + copyValue());
	}
}