基础——ArrayList集合练习0523

package cn.mmc.day14;import java.util.*;/*练习一：去除ArrayList集合中的重复元素。*/public class ExciseArrayListTest {public static void sop(Object obj){System.out.println(obj);}public static void main(String[] args) {ArrayList al = new ArrayList();al.add("java01");al.add("java02");al.add("java01");al.add("java02");al.add("java01");//al.add("java03");/*在迭代时循环中next调用一次，就要hasNext判断一次。Iterator it = al.iterator();while(it.hasNext()){sop(it.next()+"...."+it.next());}*//**/sop(al);al = singleElement(al);sop(al);}public static ArrayList singleElement(ArrayList al){//定义一个临时容器。ArrayList newAl = new ArrayList();for(Iterator it = al.iterator();it.hasNext();){Object obj = it.next();if(!newAl.contains(obj))//如果不包含ArrayList中出现的元素则加入临时容器，迭代完后返回临时容器newAl.add(obj);}return newAl;}}/* 练习二：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。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。List集合判断元素是否相同，依据是元素的equals方法。注意其它判断元素是否相同可能依据的方法不一样*/class Person{private String name;private int age;Person(String name,int age){this.name = name;this.age = age;}public boolean equals(Object obj)//重写父类的equal方法来比较两个对象是否相同{if(!(obj instanceof Person))return false;Person p = (Person)obj;//System.out.println(this.name+"....."+p.name);//在底层的操作return this.name.equals(p.name) && this.age == p.age;}/**/public String getName(){return name;}public int getAge(){return age;}}class ArrayListTest2 {public static void sop(Object obj){System.out.println(obj);}public static void main(String[] args) {ArrayList al = new ArrayList();//al.add(new Demo());al.add(new Person("lisi01",30));//al.add(Object obj);//Object obj = new Person("lisi01",30);al.add(new Person("lisi02",32));al.add(new Person("lisi02",32));al.add(new Person("lisi04",35));al.add(new Person("lisi03",33));al.add(new Person("lisi04",35));al = singleElement(al);for(Iterator it = al.iterator();it.hasNext();){Person p = (Person)it.next();sop(p.getName()+"::"+p.getAge());}sop("remove 03 :"+al.remove(new Person("lisi03",33)));//remove方法底层也是依赖于元素的equals方法。对每一个对象都进行比较for(Iterator it = al.iterator();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();for(Iterator it = al.iterator();it.hasNext();){Object obj = it.next();if(!newAl.contains(obj))//contains方法的底层原理就是类的equal方法//如果不包含ArrayList中出现的元素则加入临时容器，迭代完后返回临时容器newAl.add(obj);}return newAl;}}