Java判断一个List中是否有重复元素

1.将List转为Set，通过2个集合的size大小是否相等来判断有无重复元素

public static void main(String[] args) {
    List stringList = new ArrayList<>(Arrays.asList("a","a","b","c"));   
    Set stringSet = new HashSet<>(stringList);
    if (stringList.size() == stringSet.size()) {
        System.out.println("没有重复元素");
    } else {
        System.out.println("有重复元素");
    }
} 

2.使用jdk8的Stream来判断

public static void main(String[] args) {
    List stringList = new ArrayList<>(Arrays.asList("a","a","b","c"));
    long count = stringList.stream().distinct().count();
    if (stringList.size() == count) {
        System.out.println("没有重复元素");
    } else {
        System.out.println("有重复元素");
}