Java Foundation (LinkedList)

1. Overview of LinkedList

The ArrayList collection is very fast when querying elements , but it is less efficient when deleting . To overcome this limitation, you can use LinkedList.

LinkedList maintains a doubly circular linked list, and each element in the linked list is connected to each other. Inserting and deleting elements only need to modify the application relationship between the elements.

Features:

1. Very efficient addition and deletion
2. Low query efficiency

Second, LinkedList unique methods

Examples:

        LinkedList<String> list=new LinkedList<>();
        list.add("yyy");
        list.add("wtc");
        list.add("yyy");
        //特有的方法
        list.addFirst("aaa");//添加到列头
        list.addLast("bbb");//添加到列尾
        System.out.println(list);
        list.removeFirst();//删除列头
        list.removeLast();//删除列尾
        System.out.println(list);
        //寻找某个字符串最后出现的位置
        System.out.println("yyy最后出现的位置是"+list.lastIndexOf("yyy"));
        //推荐用迭代器去遍历
        ListIterator<String> it= list.listIterator();
        while (it.hasNext()){
            System.out.println(it.next());
        }

operation result:

3. Exercises

• Remove duplicate elements in ArrayList

import java.util.ArrayList;

public class demo_移除arraylist里的重复元素 {
    public static void main(String[] args) {
        ArrayList<String> list=new ArrayList<>();
        list.add("a");
        list.add("b");
        list.add("c");
        list.add("b");
        list.add("a");
        list.add("b");
        list.add("a");
        list.add("b");
        for(int i=0;i<list.size();i++){
            String s=list.get(i);
            for(int j=i+1;j<list.size();j++){
                String s1=list.get(j);
                if(s.equals(s1)){
                    list.remove(j);
                    j--;
                }
            }
        }
        System.out.println(list);
    }
}

operation result:

• ArrayList嵌套ArrayList

import java.util.ArrayList;

public class demo_Arraylist嵌套Arraylist {
    public static void main(String[] args) {
        ArrayList a1=new ArrayList();
        a1.add("小米");
        a1.add("小明");
        a1.add("小红");
        ArrayList a2=new ArrayList();
        a2.add("wtc");
        a2.add("yyy");
        ArrayList<ArrayList> aa=new ArrayList<>();
        aa.add(a1);
        aa.add(a2);
        for(int i=0;i<aa.size();i++){
            ArrayList arrayList=aa.get(i);
            for(int j=0;j<arrayList.size();j++){
                System.out.println(arrayList.get(j));
            }
        }
    }
}

operation result: