一般在Java中,普通类后加s即为工具类,Collections是Java中集合的工具类。
列举Collections常用的方法:
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class TestCollections {
public static void main(String[] args) {
List<String> list=new ArrayList<>();
list.add("hello");
//一次性向集合中添加元素
Collections.addAll(list,"day","come","ok");
System.out.println("原始顺序:"+list);//原始顺序:[hello, day, come, ok]
//将list乱序
Collections.shuffle(list);
System.out.println("乱序后结果:"+list); //乱序后结果:[day, ok, hello, come]
//将list反转
Collections.reverse(list);
System.out.println("反转后结果:"+list); //反转后结果:[ok, come, day, hello]
//将list填充
Collections.fill(list,"haha");
System.out.println("填充后:"+list); //填充后:[haha, haha, haha, haha]
//将list变为线程安全的集合
list=Collections.synchronizedList(list);
//将集合变为不可变集合
list=Collections.unmodifiableList(list);
list.add("en");//UnsupportedOperationException 此时,集合不可修改
}
}