List集合

一、特点、特有方法

 

import java.util.ArrayList;
import java.util.List;
 
public class ListTest1 {
    public static void main(String[] args) {
        //1.创建一个ArrayList集合对象（有序，可重复，有索引）
        List list=new ArrayList<> ();
        list.add ( "蜘蛛精" );
        list.add ( "至尊宝" );
        list.add ( "至尊宝" );
        list.add ( "牛夫人" );
        System.out.println (list);
        //2.public void add(int index ,E element) :在某个索引处插入元素
        list.add ( 2,"紫霞仙子" );
        System.out.println ( list );
        //3.public E remove(int index)  根据索引删除元素  返回被删除元素
        System.out.println ( list.remove ( 2 ) );
        System.out.println ( list );
        //4.public E get(int index):返回集合中制定位置的元素
        System.out.println ( list.get ( 3 ) );
        //5.public E set(int index,E element):修改索引位置处的元素，修改成功后，会返回原来的数据
        System.out.println ( list.set ( 3, "牛魔王" ) );
        System.out.println ( list );
    }
}

二、遍历方式（List家族通用）

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
 
public class ListTest2 {
    public static void main(String[] args) {
        List list =new ArrayList<> ();
        list.add ( "糖宝宝" );
        list.add ( "王慧饭" );
        list.add ( "大宝贝" );
        //1.for 循环
        for (int i = 0; i < list.size (); i++) {
            String s = list.get ( i );
            System.out.println ( s );
        }
        //2.迭代器
        Iterator id = list.iterator ();
        while (id.hasNext ()){
            System.out.println ( id.next () );
        }
        //3.foreach
        for (String s : list) {
            System.out.println (s);
        }
        //4.lambda表达式
        list.forEach ( s -> System.out.println (s) );
    }
}

三、ArrayList集合的底层原理，适用场景

 四、LinkedList集合的底层原理（双链表）

1.底层原理

2.应用场景

1.排队

 2.设计栈

import java.util.LinkedList;
 
public class ListTest3 {
    public static void main(String[] args) {
        //1.创建一个队列
        LinkedList queue=new LinkedList<> ();
        queue.addLast ( "第1号人" );
        queue.addLast ( "第2号人" );
        queue.addLast ( "第3号人" );
        queue.addLast ( "第4号人" );
        System.out.println ( queue );
        //出队操作
        System.out.println ( queue.removeFirst () );
        System.out.println ( queue.removeFirst () );
        System.out.println ( queue.removeFirst () );
        System.out.println ( queue );
        System.out.println ("------------------------------");
        //2.创建一个栈对象
        LinkedList stack=new LinkedList<> ();
        //压入子弹(入栈)push
        stack.addFirst ( "第1颗子弹" );
        stack.addFirst ( "第2颗子弹" );
        stack.addFirst ( "第3颗子弹" );
        stack.addFirst ( "第4颗子弹" );
        stack.push ( "第5课子弹" );//给addFirst换了个马甲
        System.out.println (stack);
        //发射子弹（出栈）pop
        System.out.println ( stack.removeFirst () );
        System.out.println ( stack.removeFirst () );
        System.out.println ( stack.removeFirst () );
        System.out.println ( stack.pop () );//给removeFirst换了个马甲
        System.out.println ( stack );
 
 
    }
}