Checking if an object is contained within a linkedlist

问题

I have this program and in the main method I add a value into a linked list. When I try to add another value through a method that checks to see if the value added previously is in the list, it does not recognize the value as being in the list and does the operation it should do if it is not in the list. Why is this program not recognizing the objects that are put into the list? the program does not recognize "h" has been added to the list.

import java.util.LinkedList;
import java.util.List;


public class Menu {
    LinkedList <LinkedList> mainMenuItems = new LinkedList <LinkedList> ();


public void  Menu(){

}

public boolean addMainMenuItem(String newItem, String existingItem, int position){
    LinkedList <String> subMenuItems = new LinkedList <String> ();
    if (! mainMenuItems.contains(existingItem)){
        subMenuItems.addLast(newItem);
        mainMenuItems.add(subMenuItems);
        return true;}
    if (mainMenuItems.contains(existingItem)){
        subMenuItems.addLast(newItem);
        int existingIndex = mainMenuItems.indexOf(existingItem);
        if (position == 1){
    LinkedList temp = new LinkedList <LinkedList>();
    temp = mainMenuItems.get(existingIndex+1);
    mainMenuItems.remove(existingIndex+1);

    mainMenuItems.add(existingIndex + 1, subMenuItems);
    mainMenuItems.add(existingIndex +2, temp);

    }


        if (position == -1){
            mainMenuItems.add(existingIndex, subMenuItems);}
    return true;    }
    return false;}


public boolean deleteMainMenuItem(String item){
    if (mainMenuItems.contains(mainMenuItems.indexOf(item))){
    mainMenuItems.remove(mainMenuItems.indexOf(item));
    return true;}
    else{
    return false;}}

public static void main(String[] args){
    Menu b = new Menu();
    b.addMainMenuItem("h", "b", 1)  ;

b.addMainMenuItem("hi", "h", 1) ;
b.addMainMenuItem("i", "h", 1)  ;
System.out.println(b.mainMenuItems.get(0));
System.out.println(b.mainMenuItems.get(1));
b.deleteMainMenuItem("hi");
System.out.println(b.mainMenuItems.get(2));
System.out.println(b.deleteMainMenuItem("hi"));


}







}

回答1:

You are testing if a String is contained by a LinkedList<LinkedList> which will always be false because a String is not the same type as a LinkedList. If you really need to test this, then you're going to have to iterate through each item in the main LinkedList and test of the String is held by any of them.

来源：https://stackoverflow.com/questions/25955973/checking-if-an-object-is-contained-within-a-linkedlist

标签

java

linked-list

contains