Question

如何比较2个List中相同的元素

Answer 1

package com.test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
*
* 找出两个list中不同的元素
* @author leiwei 2011-12-14
*
*/
public class NoEqualsElement {

public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
List<String> list2 = new ArrayList<String>();

list1.add("1");
list1.add("3");
list1.add("8");
list1.add("9");

list2.add("2");
list2.add("3");
list2.add("7");

for(String s2:list1) {
boolean flag = false;
for(String s1:list2) {
if(s2.equals(s1)) {
flag = true;
break;
}
}
if(!flag){
System.out.println(s2);
}
}
}
}

[java] view plain copy
package com.test;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import com.model.Student;

/**
* 重写对象Student的equals方法
* 只要age相等 对象就相等
*
* 删除两个集合中 相同的对象只保留一个
* @author leiwei 2011-12-19
*
*/
public class ListOBJ {

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

List<Student> list1 = new ArrayList<Student>();
List<Student> list2 = new ArrayList<Student>();

Student s1 = new Student();
s1.setAge("10");
list1.add(s1);
Student s2 = new Student();
s2.setAge("20");
list1.add(s2);

Student s3 = new Student();
s3.setAge("20");
list2.add(s3);
Student s4 = new Student();
s4.setAge("30");
list2.add(s4);

/**
* 我们知道set集合，中的元素不会重复
*
* 将连个对象集合放进去，自然就会排出重复的
*
* 对象（前提Student 对象重写了equals方法）
*/
setStudent.addAll(list1);
setStudent.addAll(list2);

//输出 测试看是否 排出成功
System.out.println(setStudent.size());

Iterator<Student> iterator = setStudent.iterator();
while (iterator.hasNext()) {
Student s = iterator.next();
System.out.println(s.getAge());
}

}
}

[java] view plain copy
package com.model;

public class Student {

private String age;

public String getAge() {
return age;
}

public void setAge(String age) {
this.age = age;
}

//重写equals方法只要age相等，我们就认为对象两个相等
@Override
public boolean equals(Object obj) {
if(obj instanceof Student){
Student st=(Student) obj;
return (age.equals(st.age));
}else{
return super.equals(obj);
}
}

@Override
public int hashCode() {

return age.hashCode();
}

}