return generic type class java code example

Example 1: generics Interface in java

/*We can define our own classes with generics type. A generic type is a class or interface that is parameterized over types. We use angle brackets (<>) to specify the type parameter.

To understand the benefit, let’s say we have a simple class as:*/
package com.journaldev.generics;

public class GenericsTypeOld {

	private Object t;

	public Object get() {
		return t;
	}

	public void set(Object t) {
		this.t = t;
	}

        public static void main(String args[]){
		GenericsTypeOld type = new GenericsTypeOld();
		type.set("Pankaj"); 
		String str = (String) type.get(); //type casting, error prone and can cause ClassCastException
	}
}

Example 2: 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);
	}