HashSet和TreeSet
package com.wzy.list; import java.util.HashSet; import java.util.Iterator; import java.util.Set; import java.util.TreeSet; class Student1 implements Comparable{ private Integer id; private String name; public Student1(String name,Integer id) { this.id = id; this.name = name; } @Override public String toString() { return "name:"+name+"; id:"+id; } @Override public int compareTo(Object o) { if(this.id > ((Student1)o).id) { return 1; }else if(this.id < ((Student1)o).id) { return -1; }else{ return this.name.compareTo(((Student1)o).name); } } } class Student2{ private Integer id; private String name; public Student2(String name,Integer id) { this.id = id; this.name = name; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Student2 other = (Student2) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } @Override public String toString() { return "Student2 [id=" + id + ", name=" + name + "]"; } } public class Test02 { public static void main(String[] args) { /** * TreeSet和HashSet存入对象时,不会自动去重操作 * * TreeSet去掉重复对象,基于Comparable接口实现 * HashSet去掉重复对象,基于equals和hashCode实现 * TreeSet可以对象排序,hashSet不可以 * * 如果存入的不是new出来的对象, * 而是String或int类型,可以直接使用,不必实现上述操作 * **/ //TreeSet存入对象实例 Set<Student1> stu1 = new TreeSet<Student1>(); stu1.add(new Student1("aa",1001)); stu1.add(new Student1("bb",1001));//id重复 stu1.add(new Student1("dd",1004)); stu1.add(new Student1("cc",1003)); stu1.add(new Student1("aa",1001));//对象重复 Iterator s = stu1.iterator(); while(s.hasNext()) { System.out.println(s.next()); } //HashSet存入对象实例 Set<Student2> stu2 = new HashSet<Student2>(); stu2.add(new Student2("aa",1001)); stu2.add(new Student2("bb",1003)); stu2.add(new Student2("cc",1005)); stu2.add(new Student2("dd",1004)); stu2.add(new Student2("ee",1002)); stu2.add(new Student2("aa",1001)); Iterator i = stu2.iterator(); while(i.hasNext()) { System.out.println(i.next()); } //TreeSet存入普通字符串 Set set1 = new TreeSet(); set1.add("a"); set1.add("aa"); set1.add("d"); set1.add("b"); set1.add("c"); //[a, aa, b, c, d] TreeSet已经自动排序好了 System.out.println(set1); //HashSet存入普通字符串 Set set2 = new HashSet(); set2.add("a"); set2.add("aa"); set2.add("d"); set2.add("c"); set2.add("b"); //[aa, a, b, c, d] HashSet不会排序 System.out.println(set2); } }
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