Custom LinkedList constructor with array as a parameter

Question

I've written this program to implement a LinkedList. There are 2 classes: Node and IntLinkedList and the relationship between them is aggregation. In the IntLinkedList class, the constructor's parameter is an array and I've tried to use a for-each loop to add the data of the array to the linked list. Here is my code:

Node.java

import java.lang.*;
public class Node {
    
    private int value;
    private Node next;
    
    public Node(){
        this.value = 0;
        this.next = null;
    }
    
    public Node(int value){
        this.value = value;
        this.next = null;
    }
    
    public Node(int value, Node next){
        this.value = value;
        this.next = next;
    }
    
    public Node getNext(){
        return this.next;
    }
    
    public int getValue(){
        return this.value;
    }
    
    public void setNext(Node next){
        this.next = next;
    }
    
    public void setValue(int value){
        this.value = value;
    }
    
    public String toString(){
        return this.value + "_" + this.next;
    }
}

IntLinkedList.java

import java.lang.*;
import java.util.*;
public class IntLinkedList {
    
    private Node head;
    
    public IntLinkedList(){
        this.head = null;
    }
    
    public IntLinkedList(int[] intArray){
        Node tmp = head;
        for (int data : intArray){
            while (tmp.getNext() != null){
                tmp.setValue(data);
                tmp = tmp.getNext();
            }
        }
    }
    
    public void printList(){
        Node tmp = head;
        while (tmp.getNext() != null){
            System.out.println(tmp.getValue() + " -> ");
            tmp = tmp.getNext();
        }
        System.out.println(tmp.getValue());
        System.out.println();
    }
    
}

I've tried for many times but it still didn't work.

You need to create a new Node object for each entry of your array. I suggest you add an add-method that adds a single element. Then in the constructor, you iterate over the int-array and call add for each entry. — Matt
– Matt, Commented Jul 22, 2021 at 7:39

ZIHAO LIU · Accepted Answer · 2021-07-22 07:39:17Z

1

In your code tmp is always null, so that when you call tmp.getNext() you will get NPE forever.

public class IntLinkedList {

    private Node head;

    public IntLinkedList() {
        this.head = null;
    }

    public IntLinkedList(int[] intArray) {
        this();
        Node tmp = head;
        for (int data : intArray) {
            if (head == null) {
                head = new Node(data);
                tmp = head;
            } else {
                tmp.setNext(new Node(data));
                tmp = tmp.getNext();
            }
        }
    }

    public void printList() {
        Node tmp = head;
        while (tmp != null) {
            System.out.println(tmp.getValue() + " -> ");
            tmp = tmp.getNext();
        }
        System.out.println();
    }
}

answered Jul 22, 2021 at 7:39

ZIHAO LIU

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