java generic in interface code example

Example 1: generics Interface in java

/*Suppose we want to restrict the type of objects that can be used in the parameterized type, for example in a method that compares two objects and we want to make sure that the accepted objects are Comparables. To declare a bounded type parameter, list the type parameter’s name, followed by the extends keyword, followed by its upper bound, similar like below method.

The invocation of these methods is similar to unbounded method except that if we will try to use any class that is not Comparable, it will throw compile-time error.

Bounded type parameters can be used with methods as well as classes and interfaces.

Java Generics supports multiple bounds also, i.e <T extends A & B & C>. In this case, A can be an interface or class. If A is class then B and C should be an interface. We can’t have more than one class in multiple bounds.*/
public static <T extends Comparable<T>> int compare(T t1, T t2){
		return t1.compareTo(t2);
	}

Example 2: generics Interface in java

/*We know that Java inheritance allows us to assign a variable A to another variable B if A is subclass of B. So we might think that any generic type of A can be assigned to generic type of B, but it’s not the case. Let’s see this with a simple program.

We are not allowed to assign MyClass<String> variable to MyClass<Object> variable because they are not related, in fact MyClass<T> parent is Object.*/
package com.journaldev.generics;

public class GenericsInheritance {

	public static void main(String[] args) {
		String str = "abc";
		Object obj = new Object();
		obj=str; // works because String is-a Object, inheritance in java
		
		MyClass<String> myClass1 = new MyClass<String>();
		MyClass<Object> myClass2 = new MyClass<Object>();
		//myClass2=myClass1; // compilation error since MyClass<String> is not a MyClass<Object>
		obj = myClass1; // MyClass<T> parent is Object
	}
	
	public static class MyClass<T>{}

}