Set实现类

• HashSet（重点）：
  • 基于HashCode计算元素存放的位置
  • 当存入元素的哈希码相同时，会调用equals进行确认，如果结果为true，则拒绝后者存入
  • 存储结构：哈希表（数组+链表+红黑树）
  • 存储过程（重复的依据）：
    1. 根据hashcode计算保存的位置，如果此位置为空，则直接保存，否则执行第二步
    2. 再执行equals方法，如果equals方法为true，则认为是重复，否则形成链表
  • HashSet存储数据实际上用的是HashMap的key来存储的

//创建集合
HashSet<String> hashSet = new HashSet<String>();//添加元素
hashSet.add("小米");
hashSet.add("苹果");
hashSet.add("华为");
hashSet.add("华为"); //不可重复
System.out.println("数据个数：" + hashSet.size()); //数据个数：3 不重复
System.out.println(hashSet.toString()); //[苹果,华为,小米] 无序//遍历
//增强for
for(String s : hashSet){System.out.println(s);
}
//迭代器
Iterator<String> it = hashSet.iterator();
while(it.hasNext()){System.out.println(it.next());
}//判断
System.out.println(hashSet.contains("OPPO")); //false
System.out.println(hashSet.isEmpty()); //false//删除数据
hashSet.remove("苹果");
System.out.println(hashSet.toString()); //[华为,小米]

//学生类
public class Student {private String name;private int age;public Student(String name, int age) {super();this.name = name;this.age = age;}public Student() {}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + "]";}//自动生成的重写方法@Overridepublic int hashCode() {//31是一个质数，减少散列冲突//31提高执行效率 31*i=(i<<5)-ifinal int prime = 31;int result = 1;result = prime * result + age;result = prime * result + ((name == null) ? 0 : name.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Student other = (Student) obj;if (age != other.age)return false;if (name == null) {if (other.name != null)return false;} else if (!name.equals(other.name))return false;return true;}//自己写的重写方法/*@Overridepublic int hashCode(){int n1 = this.name.hashCode();int n2 = this.age;return n1+n2;}@Overridepublic boolean equals(Object obj){//判断是不是同一个对象if(this == obj){return true;}//判断是否是空if(obj == null){return false;}//判断是否是Student类型if(obj instanceof Student){Student s = (Student)obj;//比较属性if(this.name.equals(s.getName()) && this.age == s.getAge()){return true;}}//不满足条件返回falsereturn false;}*/}//HashSet使用：保存学生信息
public class Test{public static void main(String[] args){//创建集合HashSet<Student> hashSet = new HashSet<Student>();Student s1 = new Student("张三",20);Student s2 = new Student("李四",21);Student s3 = new Student("王五",22);//添加数据hashSet.add(s1);hashSet.add(s2);hashSet.add(s3);hashSet.add(new Student("王五",22)); //重写hashCode、equals方法后无法添加进去，重复System.out.println("元素个数：" + hashSet.size()); //元素个数：3//遍历//1.增强for循环for(Student s : hashSet){System.out.println(s.toString());}//2.迭代器Iterator<Student> it = hashSet.iterator();while(it.hasNext()){System.out.println(it.next());}//判断System.out.println(hashSet.contains(s1)); //trueSystem.out.println(hashSet.contains(new Student("李四",21))); //重写hashCode、equals方法后返回trueSystem.out.println(hashSet.isEmpty()); //false//删除数据hashSet.remove(s1);System.out.println("删除之后：" + hashSet.size()); //删除之后：2hashSet.remove(new Student("李四",21)); //重写hashCode、equals方法才能实现删除System.out.println("删除之后：" + hashSet.size()); //删除之后：1}
}

• TreeSet
  • 基于排列顺序实现元素不重复
  • 实现了SortedSet接口，对集合元素自动排序
  • 元素对象的类型必须实现Comparable接口，指定排序规则
  • 存储结构：红黑树
  • TreeSet实际上是用的TreeMap的key来保存的值

//创建集合
TreeSet<String> treeSet = new TreeSet<String>();//添加元素
treeSet.add("xyz");
treeSet.add("abc");
treeSet.add("hello");
treeSet.add("abc"); //重复不添加
System.out.println("元素个数：" + treeSet.size()); //元素个数：3
System.out.println(treeSet.toString()); //[abc,hello,xyz]//遍历
//增强for
for(String s : treeSet){System.out.println(s);
}
//迭代器
Iterator<String> it = treeSet.iterator();
while(it.hasNext()){System.out.println(it,.next());
}//判断
System.out.println(treeSet.contains("xyz")); //true
System.out.println(treeSet.isEmpty()); //false//删除
treeSet.remove("xyz");
System.out.println("删除之后：" + treeSet.size()); //删除之后：2

//学生类
public class Student implements Comparable<Student>{private String name;private int age;public Student(String name, int age) {super();this.name = name;this.age = age;}public Student() {}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + "]";}//先按姓名比，再按年龄比@Overridepublic int compareTo(Student o) {int n1 = this.getName().compareTo(o.getName());int n2 = this.age - o.getAge();return n1==0?n2:n1;}}//TreeSet使用：保存学生信息
//元素必须要实现Comparable接口，compareTo()返回值为0即重复
public class Test{public static void main(String[] args){//创建集合TreeSet<Student> treeSet = new TreeSet<Student>();Student s1 = new Student("张三",20);Student s2 = new Student("李四",21);Student s3 = new Student("王五",22);//添加数据treeSet.add(s1);treeSet.add(s2);treeSet.add(s3);treeSet.add(new Student("王五",22)); //实现Comparable接口后无法添加进去，重复System.out.println("元素个数：" + treeSet.size()); //元素个数：3//遍历//1.增强for循环for(Student s : treeSet){System.out.println(s.toString());}//2.迭代器Iterator<Student> it = treeSet.iterator();while(it.hasNext()){System.out.println(it.next());}//判断System.out.println(treeSet.contains(s1)); //trueSystem.out.println(treeSet.contains(new Student("李四",21))); //实现Comparable接口后返回trueSystem.out.println(treeSet.isEmpty()); //false//删除数据treeSet.remove(s1);System.out.println("删除之后：" + treeSet.size()); //删除之后：2treeSet.remove(new Student("李四",21)); //实现Comparable接口才能实现删除System.out.println("删除之后：" + treeSet.size()); //删除之后：1}
}

• Comparator接口

  • 实现定制比较（比较器）

  //创建集合并指定比较规则，不用使用元素的比较规则了
  TreeSet<Student> treeSet = new TreeSet<Student>(new Comparator<Student>(){//先比年龄后比姓名@Overridepublic int compare(Student o1,Student o2){int n1 = o1.getAge() - o2.getAge();int n2 = o1.getName() - o2.getAge();return n1==0?n2:n1;}
  });
  Student s1 = new Student("张三",20);
  Student s2 = new Student("李四",21);
  Student s3 = new Student("王五",22);//添加数据
  treeSet.add(s1);
  treeSet.add(s2);
  treeSet.add(s3);
  treeSet.add(new Student("王五",22)); //实现Comparator接口的compare方法后无法添加进去，重复
  System.out.println("元素个数：" + treeSet.size()); //元素个数：3
  

  TreeSet<String> treeSet = new TreeSet<String>(new Comparator<String>(){//按照字符串长度进行比较@Overridepublic int compare(String o1,String o2){int n1 = o1.length() - o2.length();int n2 = o1.compareTo(o2);return n1==0?n2:n1;}
  });