java

list集合去除重复对象

对象重复是指对象里面的变量的值都相等，并不定是地址。list集合存储的类型是基础类型还比较好办，直接把list集合转换成set集合就会自动去除。

当set集合存储的是对象类型时，需要在对象的实体类里面重写public boolean equals(Object obj) {} 和 public int hashCode() {} 两个方法。

实体类

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
public class Student {  
  
    public String id;  
    public String name;  
    public Student() {  
    }  
    public Student(String id,String name) {  
        this.id = id;  
        this.name = name;  
    }  
    public String getId() {  
        return id;  
    }  
    public void setId(String id) {  
        this.id = id;  
    }  
    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  
    @Override  
    public boolean equals(Object obj) {  
        Student s=(Student)obj;   
        return id.equals(s.id) && name.equals(s.name);   
    }  
    @Override  
    public int hashCode() {  
        String in = id + name;  
        return in.hashCode();  
    }  
}

测试类

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
import java.util.ArrayList;  
import java.util.HashSet;  
import java.util.List;  
import java.util.Set;  
  
public class QuSame {  
      
    public static void main(String[] args) {  
        List<Student> stu = new ArrayList<Student>();  
        stu.add(new Student("1","yi"));  
        stu.add(new Student("3","san"));  
        stu.add(new Student("3","san"));  
        stu.add(new Student("2","er"));  
        stu.add(new Student("2","er"));  
        //set集合保存的是引用不同地址的对象  
        Set<Student> ts = new HashSet<Student>();  
        ts.addAll(stu);  
          
        for (Student student : ts) {  
            System.out.println(student.getId()+"-"+student.getName());  
        }  
    }  
}