import java.util.*; public class TreeSetDemo { public static void main(String[] args) { //过滤重复元素，但不保证元素的迭代次序 String[] strArray = new String[]{"one", "world ", "one", "dream"}; Set<String> s = new HashSet<String>(); for (int i=0; i<4; i++) if (!s.add(strArray[i])) //添加strArray元素到集合s中 System.out.println("Duplicate detected: " + strArray[i]); System.out.println(s.size() + " distinct words: " + s); //自动按升序排列内容 并过滤掉重复元素 TreeSet<String> treeset=new TreeSet<String>(); treeset.add("b"); treeset.add("a"); 【代码1】： treeset.add("d"); treeset.add("b"); System.out.println("TreeSet:"); System.out.println(treeset); System.out.println("the first element is: "+treeset.first());//返回第一个元素 【代码2】： while(iterator.hasNext()){ System.out.print(iterator.next()+";"); } } }

完整的代码应该是这样的：

import java.util.*;

public class TreeSetDemo {
    public static void main(String[] args) {
        //过滤重复元素，但不保证元素的迭代次序
        String[] strArray = new String[]{"one", "world ", "one", "dream"};
        Set<String> s = new HashSet<String>();
        for (int i = 0; i < 4; i++)
            if (!s.add(strArray[i])) //添加strArray元素到集合s中
                System.out.println("Duplicate detected: " + strArray[i]);
        System.out.println(s.size() + " distinct words: " + s);

        //自动按升序排列内容 并过滤掉重复元素
        TreeSet<String> treeset = new TreeSet<String>();
        treeset.add("b");
        treeset.add("a");
        treeset.add("d");
        treeset.add("b");
        System.out.println("TreeSet:");
        System.out.println(treeset);
        System.out.println("the first element is: " + treeset.first());

        //使用迭代器遍历集合
        Iterator<String> iterator = treeset.iterator();
        System.out.println("TreeSet Elements:");
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + ";");
        }
    }
}

运行结果为：

Duplicate detected: one
4 distinct words: [dream, one, world ]
TreeSet:
[a, b, d]
the first element is: a
TreeSet Elements:
a;b;d;