Set添加自定义方法对象如何保证唯一性

一、通过查看add方法的源码，我们知道这个方法底层依赖两个方法：hashCode()和equals()。如果类没有重写这两个方法，默认使用的Object()。一般来说仅仅hashCode可能都不会相同，equals也不相同；则会全部添加到集合中去。
* 例如自定义对象没有重写hashCode()和equals()方法的时候，就全部打印出来。这也是不重复的原因。
* 而String类（写字符串对象的时候）重写了hashCode()和equals()方法，所以，它就可以把内容相同的字符串去掉。

实体类没有hashCode()和equals()方法的时候

public class Student {

   private String name;
   private String password;
  public Student() {
       super();
       // TODO Auto-generated constructor stub
   }

   public Student(String name, String password) {
       super();
       this.name = name;
       this.password = password;
   }

   public String getName() {
       return name;
   }
   public void setName(String name) {
       this.name = name;
   }
   public String getPassword() {
       return password;
   }
   public void setPassword(String password) {
       this.password = password;
   }


   /*@Override
   public int hashCode() {
       final int prime = 31;
       int result = 1;
       result = prime * result + ((name == null) ? 0 : name.hashCode());
       result = prime * result
               + ((password == null) ? 0 : password.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;
       Student other = (Student) obj;
       if (name == null) {
           if (other.name != null)
               return false;
       } else if (!name.equals(other.name))
           return false;
       if (password == null) {
           if (other.password != null)
               return false;
       } else if (!password.equals(other.password))
           return false;
       return true;
   }*/

   public static void main(String[] args) {
       Set<Student> set = new HashSet<Student>();

       set.add(new Student("yj","123"));
       set.add(new Student("yj","123"));
       set.add(new Student("yc","123"));
       set.add(new Student("yc","123"));

       for (Student ob : set) {
           System.out.println(ob.getName()+"---"+ob.getPassword());
       }

   }

}
实体类没有hashCode()和equals()方法的时候运行打印的结果

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实体类有hashCode()和equals()方法的时候

package it.fuxi;

import java.util.HashSet;
import java.util.Set;

public class Student {

   private String name;
   private String password;




   public Student() {
       super();
       // TODO Auto-generated constructor stub
   }

   public Student(String name, String password) {
       super();
       this.name = name;
       this.password = password;
   }

   public String getName() {
       return name;
   }
   public void setName(String name) {
       this.name = name;
   }
   public String getPassword() {
       return password;
   }
   public void setPassword(String password) {
       this.password = password;
   }


   @Override
   public int hashCode() {
       final int prime = 31;
       int result = 1;
       result = prime * result + ((name == null) ? 0 : name.hashCode());
       result = prime * result
               + ((password == null) ? 0 : password.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;
       Student other = (Student) obj;
       if (name == null) {
           if (other.name != null)
               return false;
       } else if (!name.equals(other.name))
           return false;
       if (password == null) {
           if (other.password != null)
               return false;
       } else if (!password.equals(other.password))
           return false;
       return true;
   }

   public static void main(String[] args) {
       Set<Student> set = new HashSet<Student>();

       set.add(new Student("yj","123"));
       set.add(new Student("yj","123"));
       set.add(new Student("yc","123"));
       set.add(new Student("yc","123"));

       for (Student ob : set) {
           System.out.println(ob.getName()+"---"+ob.getPassword());
       }

   }

}

实体类有hashCode()和equals()方法的时候运行打印的结果

Set添加自定义方法对象如何保证唯一性

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