ArrayList的contains方法，底层调用了equals方法。

题目：

将自定义对象作为元素存到ArrayList集合中，并去除重复元素

比如：存人对象，同姓名，同年龄，视为同一个人，为重复元素。

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/* 思路 1对人描述，将数据封装进人对象 2定义容器，将人存入 3取出 */ import java.util.*; class Person {         private String name;         private int age;         Person(String name,int age)         {                 this.name= name;                 this.age= age;         }         public boolean equals(Object obj)         {                 if(!(obj instanceof Person))                         return false;                   Person p= (Person)obj;                 return this.name.equals(p.name)&& this.age == p.age;         }         public String getName()         {                 return name;         }         public int getAge()         {                 return age;         } }   class Test {         public static void main(String[] args)         {                 ArrayList al = new ArrayList();                   al.add(new Person("lisi01",30));                 al.add(new Person("lisi02",35));                 al.add(new Person("lisi03",32));                 al.add(new Person("lisi02",35));                 al.add(new Person("lisi03",32));                 al.add(new Person("lisi04",31));                   al=singleElement(al);                   Iterator it = al.iterator();                   while (it.hasNext())                 {                         Person p = (Person)it.next();                         sop(p.getName()+"---"+p.getAge());                 }         }           public static ArrayList singleElement(ArrayList al)         {                 //定义一个临时容器                 ArrayList newAl = new ArrayList();                 Iterator it =al.iterator();                                   while (it.hasNext())                 {                         Object obj = it.next();                         if (!newAl.contains(obj))                                 newAl.add(obj);                 }                 return newAl;         }           public static void sop(Object obj)         {                 System.out.println(obj);         } }

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public boolean contains(Object o) {         return indexOf(o) >= 0;     }     public int indexOf(Object o) {         if (o == null) {             for (int i = 0; i < size; i++)                 if (elementData[i]==null)                     return i;         } else {             for (int i = 0; i < size; i++)                 if (o.equals(elementData[i]))    //调用参数的equals方法                     return i;         }         return -1;     }

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