generics in java method

// generic methods public <T> List<T> fromArrayToList(T[] a) { return Arrays.stream(a).collect(Collectors.toList()); } public static <T, G> List<G> fromArrayToList(T[] a, Function<T, G> mapperFunction) { return Arrays.stream(a) .map(mapperFunction) .collect(Collectors.toList()); } // bounded generics public <T extends Number> List<T> fromArrayToList(T[] a) { ... } //multiple bounds <T extends Number & Comparable> // upper bound wildcards public static void paintAllBuildings(List<? extends Building> buildings) { ... } // lower bound wildcard <? super T>

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
	}
}

Posted by: Guest on December-06-2020

Source

/*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 } }

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