类型参数原因错误

Question

I have this class as follows :-

import java.util.*;
public class QueueTest<T>{

    Queue<T> q = new LinkedList<T>();
    int capacity;

    public QueueTest(int capacity){
        this.capacity = capacity;
    }

    **public <T> void put(T item) throws InterruptedException**{
        while(q.size()== capacity){
            System.out.println("Now Queue is full and i will wait");
            wait();
        }
        q.add(item);
        System.out.println("I added : "+item);
        notify();
    }

    public T got() throws InterruptedException{
        while(q.isEmpty()){
            System.out.println("Now Queue is empty and i will wait ");
            wait();
        }
        T item = q.remove();
        System.out.println("I got : "+item);
        notify();
        return item;
    }
}

the declaration of method put() cause this error ??

QueueTest.java:17: error: no suitable method found for add(T#1)
                q.add(item);

and when I remove T , the class compiled without errors, but I don't know why ???

Answer 1

Get rid of the T in

public <T> void put(T item) throws InterruptedException{
        ^

If you leave it, you are declaring a different type variable that is shadowing your class' type variable T . You can bind a different type to this one, so the compiler cannot guarantee that it will be the same as the one bound to the Queue . You seem to want to use the same type variable as the one the in the class declaration.