Custom LinkedList constructor with array as a parameter

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.

Answer

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();
    }
}