十、Collections工具类

public class TestCollections {
    public static void main(String[] args) {
        ArrayList<String> al=new ArrayList<String>();
        //向集合中一次性添加N多个元素
        Collections.addAll(al, "hello","world","java");
        System.out.println(al);//[hello, world, java]
        
        //排序
        Collections.sort(al);//为什么按照英文字母的升序排序？因为String类具备了比较大小的能力
        System.out.println(al);         //[hello, java, world]
        
        //二分搜索
        System.out.println(Collections.binarySearch(al, "java"));//1
        System.out.println(Collections.binarySearch(al, "html"));//-2 -2= -(插入点+1) 推理出来插入点 1
        
        //集合拷贝
        ArrayList<String> al2=new ArrayList<String>();
        Collections.addAll(al2, "sql","sql","sql","sql4");
        //集合拷贝注意的地方:如果源集合.size()>目标集合的.size()   IndexOutOfBoundsException
        Collections.copy(al2, al); //将al中所有元素拷贝到al2中,[hello, java, world, sql4]
        System.out.println(al2);
        
        //填 充
        Collections.fill(al2, "html");//[html, html, html, html]
        System.out.println(al2);
        
        //最大与最小
        System.out.println("最大:"+Collections.max(al));//最大:world
        System.out.println("最小:"+Collections.min(al));//最小:hello
        
        //逆序
        Collections.reverse(al);
        System.out.println(al);//[world, java, hello]
        
        //线程同步
        List<String> list=Collections.synchronizedList(al);
    }
}