Collections类

rt.jar/java.util包下

public class Collections

集合工具类

1、Collections创建的集合,不支持add方法添加元素;故在实际工作中建集合用对应类实例化得到集合
2、可用Collections类操作List,Set集合

//创建list集合，addAll添加元素
public static  boolean addAll(Collection c, T... elements)

List list = new ArrayList();
Collections.addAll(list, "D","C","B","A");
for (String value : list) {
	System.out.println("list集合内元素 = " + value);
}

//sort方法 对集合排序
public static > void sort(List list)

Collections.sort(list);
for (String value : list) {
	System.out.println("list集合sort后元素 = " + value);
}

//binarySearch 搜索元素名并输出其下标
public static 
    int binarySearch(List> list, T key)

System.out.println("A index = " + Collections.binarySearch(list, "A"));

//reverse 集合内元素反转
public static void reverse(List list)

Collections.reverse(list);
for (String value : list) {
	System.out.println("list集合reverse后元素 = " + value);
}

//swap 交换指定位置的内容
public static void swap(List list, int i, int j)

Collections.swap(list, 0, 3);
for (String value : list) {
    System.out.println("list集合swap后元素 = " + value);
}

//replaceAll 全替换
public static  boolean replaceAll(List list, T oldVal, T newVal)

System.out.println("A替换为AA结果为 = " + Collections.replaceAll(list, "A", "AA"));
for (String value : list) {
    System.out.println("list集合replaceAll后元素 = " + value);
}

//min 集合中第1个元素
public static > T min(Collection coll)

System.out.println("集合中min = " + Collections.min(list));

//max 集合中最后1个元素
public static > T max(Collection coll)

System.out.println("集合中max = " + Collections.max(list));