package org.code2care.generics;
public class Example<T extends Number> {
public static void main(String[] args) {
Example<String> example = new Example<String>();
}
}
Compilation Error:
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>();
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Rakesh (He/Him) has over 14+ years of experience in Web and Application development. He is the author of insightful How-To articles for Code2care.
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