HashSet和TreeSet有什么区别？

参考代码： HashSetTest TreeSetTest TreeSetStudentTest

// Set的使用(不允许有重复的对象),可以是null,但只能放入一个null public class HashSetTest { public static void main(String[] args) { HashSet 
  
    hashSet = new HashSet 
   
     (); String a = new String("A"); String b = new String("B"); String E = new String("E"); String F = new String("F"); String c = new String("B"); String h = null; String i = null; hashSet.add(a); hashSet.add(b); hashSet.add(E); hashSet.add(F); hashSet.add(h); hashSet.add(i); System.out.println("hashSet得长度：" + hashSet.size()); // 元素B已经存在，插入时不在插入 String cz = hashSet.add(c) ? "此对象不存在" : "已经存在"; System.out.println("测试是否可以添加对象: " + cz); // 测试其中是否已经包含某个对象 System.out.println("hashSet中包含A：" + hashSet.contains("A")); Iterator 
    
      iter = hashSet.iterator(); while (iter.hasNext()) { System.out.println("hashSet中的元素：" + iter.next()); } // 测试某个对象是否可以删除 System.out.println("删除不存在的元素e:" + hashSet.remove("e")); System.out.println("删除存在的元素E:" + hashSet.remove("E")); System.out.println(); // 如果你想再次使用iter变量,必须重新更新,重新获取 iter = hashSet.iterator(); while (iter.hasNext()) { System.out.println("删除存在的元素E后:" + iter.next()); } } } 
     
    
  

// 有序的 public class TreeSetTest { public static void main(String[] args) { TreeSet 
  
    tree = new TreeSet 
   
     (); tree.add("China"); tree.add("America"); tree.add("Japan"); tree.add("Chinese"); tree.add("Diio"); Iterator 
    
      iter = tree.iterator(); while (iter.hasNext()) { System.out.println(iter.next()); } } } 
     
    
  

/ * 测试TreeSet存储自定义对象，并对对象排序的两种方式 */ public class TreeSetStudentTest { public static void main(String[] args) { System.out.println("下面是元素实现Comparable接口====="); TreeSet 
  
    ts = new TreeSet 
   
     (); ts.add(new Student("zhangsan01", 25)); ts.add(new Student("zhangsan02", 21)); ts.add(new Student("zhangsan03", 18)); ts.add(new Student("zhangsan04", 26)); ts.add(new Student("zhangsan04", 27)); ts.add(new Student("zhangsan04", 27)); ts.add(new Student("zhangsan05", 50)); Iterator 
    
      it = ts.iterator(); while (it.hasNext()) { Student stu = (Student) it.next(); System.out.println("姓名：" + stu.getName() + " 年龄：" + stu.getAge()); } System.out.println("下面是用自定义比较器类来实现比较的====="); TreeSet 
     
       tsc = new TreeSet 
      
        (new MyCompare()); tsc.add(new Student("zhangsan01", 25)); tsc.add(new Student("zhangsan02", 21)); tsc.add(new Student("zhangsan03", 18)); tsc.add(new Student("zhangsan04", 26)); tsc.add(new Student("zhangsan04", 27)); tsc.add(new Student("zhangsan04", 27)); tsc.add(new Student("zhangsan05", 50)); Iterator 
       
         itc = tsc.iterator(); while (itc.hasNext()) { Student stu = (Student) itc.next(); System.out.println("姓名：" + stu.getName() + " 年龄：" + stu.getAge()); } } } class Student implements Comparable