Fix: type argument is not within bounds of type-variable T

package org.code2care.generics;

public class Example<T extends Number> {

    public static void main(String[] args) {

        Example<String> example = new Example<String>();
    }
}

Example.java:7: error: type argument String is not within bounds of type-variable T
        Example<String> example = new Example<String>();
                ^
  where T is a type-variable:
    T extends Number declared in class Example
Example.java:7: error: type argument String is not within bounds of type-variable T
        Example<String> example = new Example<String>();
                                              ^
  where T is a type-variable:
    T extends Number declared in class Example
2 errors

Here, we are dealing with bounded type generics (T extends Number) in Java.

Why this error?

In our case, we should have type T to be a subtype of Number, or its upper bound can be the Number itself. As String is not a type of Number hence we get this compilation error.

Fix

You have to make sure that the type that you use with extends should be a subtype of the upper-bound specified or the upper-bound class type itself.

So in our case, we have some of the following possibilities.

Client<Byte> byteType = new Client<Byte>();
Client<Short> shortType = new Client<Short>();
Client<Integer> intType = new Client<Integer>();
Client<Long> longType = new Client<Long>();
Client<Double> doubleType = new Client<Double>();

Client<Number> numberType = new Client<Number>();