Generics in java, extending interfaces

Question

In the code below:

class A<T extends InterfaceA & InterfaceB>

what does it mean "T should be a type of InterfaceA"?

for example the next code:

class A<T extends Number>

means that T can be an int, a double or any other numeric types. can anyone give me an example to explain the first code?

Answer 1

class A<T extends interfaceA & interfaceB> means

that T is bounded by two interfaces. Thus,any type argument passed to T must implement interfaceA and interfaceB.

Sample program for your understanding :-

interface X{
public void eat();
}

interface Y{
public void drink();
}

class XYZ implements X,Y{
@Override
public void eat(){
    System.out.println("I am eating.");   
}
@Override
public void drink(){
    System.out.println("I am drinkin too!");
}    
}

class A<T extends X & Y> {
public void display(){
     XYZ x=new XYZ();
     x.eat();
     x.drink();
     System.out.println("Type of XYZ is "+x.getClass().getName());
    }  
}

public class Sample1{
public static void main(String[] args) {
 A<XYZ> a=new A<>();
 a.display();
}    
}

This means that type which argument passed to T must implement interfaces X and Y.

Like shown in the given code :-

A<XYZ> a=new A<>(); //here only XYZ(substituted in place of T) can be passed because it implements both interface X and interface Y

I hope this much helps you understand and point out the differences!!!