性能优化之ArrayList

ArrayListTest 写道

package cn.com;

import java.util.ArrayList;

/**
*
* @ClassName: ArrayListTest
* @Description: 大容量性能测试 
* @author linsky328
* @date 2017年6月22日 下午2:31:25
*
*/
public class ArrayListTest {

private final static int SIZE = 10000000;

/**
*
* @param args
*/
public static void main(String[] args) {

Object obj = new Object();
ArrayList<Object> list = new ArrayList<Object>();

long a1 = System.currentTimeMillis();
for (int i = 0; i < SIZE; i++) {
list.add(obj);
}
long a2 = System.currentTimeMillis();
System.out.println("costs:" + (a2 - a1) + "ms");



list = new ArrayList<Object>();
a1 = System.currentTimeMillis();
// 调用ensureCapacity预先设置大小
list.ensureCapacity(SIZE);
for (int i = 0; i < SIZE; i++) {
list.add(obj);
}
a2 = System.currentTimeMillis();
System.out.println("costs:" + (a2 - a1) + "ms");
}

}