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How to function a value in a Generic function in java?

Getting error: incompatible types: int cannot be converted to T. I want to build a queue using linked list that can store items of different data types. Please suggest ways on how can i pass values belonging to different data types into the generic function add().

public void main(String args[])
{
    MyQueue<T> q=new MyQueue<T>();
    q.add(10);
    q.add("Hello");
}

public void add(T item)
{
    QueueNode<T> t=new QueueNode<T>(item);
    if(last!=null)
    {
        last.next=t;
    }
    last=t;
}

7 months ago · Santiago Trujillo

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Answer 1 · 2022-04-20T18:09:19.815Z

T is a placeholder for a Type, but you can't declare T like this since T must be a known type. You want something like this. Here T is a known type which is passed to QueueNode and MyQueue.

package com.company;

import java.util.ArrayList;
import java.util.List;

class QueueNode<T> {
    private T nodeVal;

    T getNodeVal() {
        return nodeVal;
    }

    void setNodeVal(T nodeVal) {
        this.nodeVal = nodeVal;
    }

    QueueNode(T nodeVal) {
        this.nodeVal = nodeVal;
    }
}

class MyQueue<T> {
    private List<QueueNode<T>> actualQueue = new ArrayList<QueueNode<T>>();

    public List<QueueNode<T>> getActualQueue() {
        return actualQueue;
    }

    public void enqueue(T t) {
        actualQueue.add(new QueueNode<>(t));
    }

    public QueueNode<T> dequeue() {
        return actualQueue.remove(0);
    }
}

class Main {

    public static void main(String[] args) {

        MyQueue<Integer> integerQueue = new MyQueue<Integer>();
        integerQueue.enqueue(1);
        integerQueue.enqueue(2);
        integerQueue.enqueue(3);
        integerQueue.getActualQueue().forEach(e -> System.out.print(e.getNodeVal() + " ")); //prints 1 2 3
        System.out.println(); 
        integerQueue.dequeue();
        integerQueue.getActualQueue().forEach(e -> System.out.print(e.getNodeVal() + " ")); //prints 2 3
        System.out.println(); 
        integerQueue.dequeue();
        integerQueue.getActualQueue().forEach(e -> System.out.print(e.getNodeVal() + " ")); //prints 3
        System.out.println(); 
    }
}

Answer 2 · 2022-04-20T18:09:19.822Z

You should change de T for Object. This way you can place whatever data type you want and then you can use a foreach, for example:

public static void main(String args[])
{
    Queue<Object> queues=new LinkedList<>();
    queues.add(10);
    queues.add("Hello");

    for(Object queue:queues){
        System.out.println(queue);
    }
}

The Generic class gives solution more bigger.

Also consider that int is a primitive data type and it's not a class. In this case Integer is the class that uses int.