In this tutorial, we will learn about Java Generics, how to create generics class and methods and its advantages with the help of examples.<\/p>\n\n\n\n
The Java Generics allows us to create a single class, interface, and method that can be used with different types of data (objects).<\/p>\n\n\n\n
This helps us to reuse our code.<\/p>\n\n\n\n
Note<\/strong>: Generics<\/strong> does not work with primitive types ( We can create a class that can be used with any type of data. Such a class is known as Generics Class.<\/p>\n\n\n\n Here’s is how we can create a generics class in Java:<\/p>\n\n\n\n Output<\/strong><\/p>\n\n\n\n In the above example, we have created a generic class named GenericsClass<\/var>. This class can be used to work with any type of data.<\/p>\n\n\n\n Here, T<\/var> used inside the angle bracket Similar to the generics class, we can also create a method that can be used with any type of data. Such a class is known as Generics Method.<\/p>\n\n\n\n Here’s is how we can create a generics class in Java:<\/p>\n\n\n\n Output<\/strong><\/p>\n\n\n\n In the above example, we have created a generic method named genericsMethod<\/var>.<\/p>\n\n\n\n Here, the type parameter We can call the generics method by placing the actual type Note<\/strong>: We can call the generics method without including the type parameter. For example,<\/p>\n\n\n\n In this case, the compiler can match the type parameter based on the value passed to the method.<\/p>\n\n\n\n In general, the type parameter<\/strong> can accept any data types (except primitive types).<\/p>\n\n\n\n However, if we want to use generics for some specific types (such as accept data of number types) only, then we can use bounded types.<\/p>\n\n\n\n In the case of bound types, we use the This means T<\/var> can only accept data that are subtypes of A<\/var>.<\/p>\n\n\n\n In the above example, we have created a class named GenericsClass. Notice the expression, notice the expression<\/p>\n\n\n\n Here, GenericsClass<\/var> is created with bounded type. This means GenericsClass<\/var> can only work with data types that are children of However, we have created an object of the generics class with With the help of generics in Java, we can write code that will work with different types of data. For example,<\/p>\n\n\n\n Here, we have created a generics method. This same method can be used to perform operations on integer data, string data, and so on.<\/p>\n\n\n\n The type parameter<\/strong> of generics provides information about the type of data used in the generics code. For example,<\/p>\n\n\n\n Here, we know that GenericsClass<\/var> is working with Now, if we try to pass data other than Integer to this class, the program will generate an error at compile time.<\/p>\n\n\n\n The collections framework uses the concept of generics in Java. For example,<\/p>\n\n\n\nint<\/code>, float<\/code>, char<\/code>, etc).<\/p>\n\n\n\n
\n\n\n\nJava Generics Class<\/h2>\n\n\n\n
Example: Create a Generics Class<\/h3>\n\n\n\n
class Main {\n public static void main(String[] args) {\n\n \/\/ initialize generic class\n \/\/ with Integer data\n GenericsClass<Integer> intObj = new GenericsClass<>(5);\n System.out.println(\"Generic Class returns: \" + intObj.getData());\n\n \/\/ initialize generic class\n \/\/ with String data\n GenericsClass<String> stringObj = new GenericsClass<>(\"Java Programming\");\n System.out.println(\"Generic Class returns: \" + stringObj.getData());\n }\n}\n\n\/\/ create a generics class\nclass GenericsClass<T> {\n\n \/\/ variable of T type\n private T data;\n\n public GenericsClass(T data) {\n this.data = data;\n }\n\n \/\/ method that return T type variable\n public T getData() {\n return this.data;\n }\n}<\/code><\/pre>\n\n\n\nGeneric Class returns: 5\nGeneric Class returns: Java Programming<\/samp><\/code><\/pre>\n\n\n\nclass GenericsClass<T> {...}<\/code><\/pre>\n\n\n\n<><\/code> indicates the type parameter<\/strong>. Inside the Main<\/code> class, we have created two objects of GenericsClass<\/var><\/p>\n\n\n\nInteger<\/code>. Now, the GenericsClass<\/var> works with integer data.<\/li>String<\/code>. Now, the GenericsClass<\/var> works with string data.<\/li><\/ul>\n\n\n\n
\n\n\n\nJava Generics Method<\/h2>\n\n\n\n
Example: Create a Generics Method<\/h3>\n\n\n\n
class Main {\n public static void main(String[] args) {\n\n \/\/ initialize the class with Integer data\n DemoClass demo = new DemoClass();\n\n \/\/ generics method working with String\n demo.<String>genericsMethod(\"Java Programming\");\n\n \/\/ generics method working with integer\n demo.<Integer>genericsMethod(25);\n }\n}\n\nclass DemoClass {\n\n \/\/ creae a generics method\n public <T> void genericsMethod(T data) {\n System.out.println(\"Generics Method:\");\n System.out.println(\"Data Passed: \" + data);\n }\n}<\/code><\/pre>\n\n\n\nGenerics Method:\nData Passed: Java Programming\nGenerics Method:\nData Passed: 25<\/samp><\/code><\/pre>\n\n\n\npublic <T> void genericMethod(T data) {...}<\/code><\/pre>\n\n\n\n<T><\/code> is inserted after the modifier public<\/code> and before the return type void<\/code>.<\/p>\n\n\n\n<String><\/code> and <Integer><\/code> inside the bracket before the method name.<\/p>\n\n\n\ndemo.<String>genericMethod(\"Java Programming\");\n\ndemo.<Integer>genericMethod(25);<\/code><\/pre>\n\n\n\ndemo.genericsMethod(\"Java Programming\");<\/code><\/pre>\n\n\n\n
\n\n\n\nBounded Types<\/h2>\n\n\n\n
extends<\/code> keyword. For example,<\/p>\n\n\n\n<T extends A><\/code><\/pre>\n\n\n\nExample: Bounded Types<\/h3>\n\n\n\n
class GenericsClass <T extends Number> {\n\n public void display() {\n System.out.println(\"This is a bounded type generics class.\");\n }\n}\n\nclass Main {\n public static void main(String[] args) {\n\n \/\/ create an object of GenericsClass\n GenericsClass<String> obj = new GenericsClass<>();\n }\n}<\/code><\/pre>\n\n\n\n<T extends Number> <\/code><\/pre>\n\n\n\nNumber<\/code> (Integer<\/code>, Double<\/code>, and so on).<\/p>\n\n\n\nString<\/code>. In this case, we will get the following error.<\/p>\n\n\n\nGenericsClass<String> obj = new GenericsClass<>();\n ^\n reason: inference variable T has incompatible bounds\n equality constraints: String\n lower bounds: Number\n where T is a type-variable:\n T extends Number declared in class GenericsClass<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nAdvantages of Java Generics<\/h2>\n\n\n\n
1. Code Reusability<\/h3>\n\n\n\n
public <T> void genericsMethod(T data) {...}<\/code><\/pre>\n\n\n\n2. Compile-time Type Checking<\/h3>\n\n\n\n
\/\/ using Generics\nGenericsClass<Integer> list = new GenericsClass<>();<\/code><\/pre>\n\n\n\nInteger<\/code> data only.<\/p>\n\n\n\n3. Used with Collections<\/h3>\n\n\n\n
\/\/ creating a string type ArrayList\nArrayList<String> list1 = new ArrayList<>();\n\n\/\/ creating a integer type ArrayList\nArrayList<Integer> list2 = new ArrayList<>();<\/code><\/pre>\n\n\n\n