Collection的retainAll和equals方法：

package com.cheng.collection;
​
import java.util.ArrayList;
import java.util.Collection;
​
​
//coll.retainAll(coll1)  取coll和coll1集合的交集 並返回給coll（當前集合）
//equals 判斷兩集合內容是否相等
public class RetainAndEquals {
  public static void main(String[] args) {
    Collection coll = new ArrayList();
    coll.add(123);
    coll.add(456);
    coll.add(123);
    coll.add(new String("牛不牛"));
    coll.add(false);
    coll.add(new Person("Ali",24));
​
    Collection coll1 = new ArrayList();
    coll1.add(123);
    coll1.add(new String("牛不牛"));
    coll1.add(new Person("Ali",24));
​
    coll.retainAll(coll1);//取交集
    System.out.println(coll);//[123, 123, 牛不牛, Person{name='Ali', age=24}]
​
    Collection coll2 = new ArrayList();
    coll2.add(123);
    coll2.add(456);
    coll2.add(new String("牛不牛"));
    coll2.add(false);
    coll2.add(new Person("Ali",24));
​
    System.out.println(coll.equals(coll2));//false
    // 注意 此處是ArrlyList有序放的元素  若是元素一樣但是順序不一致也是false
​
​
   }
}
​
 

Person類：

package com.cheng.collection;
​
import java.util.Objects;
​
public class Person {
  private String name;
  private int age;
​
  public Person() {
   }
​
  public Person(String name, int age) {
    this.name = name;
    this.age = age;
   }
​
  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;
   }
​
  @Override
  public String toString() {
    return "Person{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
   }
​
​
  //重寫equals如下
  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Person person = (Person) o;
    return age == person.age && Objects.equals(name, person.name);
   }
​
​
​
}
​