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

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();
}
}

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

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());
        }
    }
}