java generic interface example

Example 1: generics Interface in java

/*Notice that while using this class, we have to use type casting and it can produce ClassCastException at runtime. Now we will use java generic class to rewrite the same class as shown below.*/
package com.journaldev.generics;

public class GenericsType<T> {

	private T t;
	
	public T get(){
		return this.t;
	}
	
	public void set(T t1){
		this.t=t1;
	}
	
	public static void main(String args[]){
		GenericsType<String> type = new GenericsType<>();
		type.set("Pankaj"); //valid
		
		GenericsType type1 = new GenericsType(); //raw type
		type1.set("Pankaj"); //valid
		type1.set(10); //valid and autoboxing support
	}
}
/*Notice the use of GenericsType class in the main method. We don’t need to do type-casting and we can remove ClassCastException at runtime. If we don’t provide the type at the time of creation, the compiler will produce a warning that “GenericsType is a raw type.

References to generic type GenericsType<T> should be parameterized”. When we don’t provide the type, the type becomes Object and hence it’s allowing both String and Integer objects. But, we should always try to avoid this because we will have to use type casting while working on raw type that can produce runtime errors.

Tip: We can use @SuppressWarnings("rawtypes") annotation to suppress the compiler warning, check out java annotations tutorial.*/

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);
	}