Angle Bracket in Java with Examples

Angle Bracket in Java is used to define Generics. It means that the angle bracket takes a generic type, say T, in the definition and any class as a parameter during the calling. The idea is to allow type (Integer, String, … etc and user-defined types) to be a parameter to methods, classes, and interfaces. For example, classes like HashSet, ArrayList, HashMap, etc use generics very well. We can use them for any type.

Example:

<T> // of type T
<Integer> // of type Integer
<String> // of type String
<MyClass> // of type MyClass
.
.

How to use angle bracket with Class?:

We use angle brackets ‘<>’ to specify parameter types in generic class creation. To create objects of a generic class, we use the following syntax:

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// To create an instance of generic class 
BaseType  obj = new BaseType ()

Note: In Parameter type,
      we can not use primitives like 
      'int', 'char' or 'double'.

// A Simple Java program 
// to show working of user defined 
// Generic classes 

// We use < > to specify Parameter type 
class Test<T> { 

	// An object of type T is declared 
	T obj; 

	// constructor 
	Test(T obj) 
	{ 
		this.obj = obj; 
	} 

	public T getObject() 
	{ 
		return this.obj; 
	} 
} 

// Driver class to test above 
class Main { 
	public static void main(String[] args) 
	{ 
		// instance of Integer type 
		Test<Integer> iObj 
			= new Test<Integer>(15); 
		System.out.println(iObj.getObject()); 

		// instance of String type 
		Test<String> sObj 
			= new Test<String>("OnlineITGuru"); 
		System.out.println(sObj.getObject()); 
	} 
} 

Output:

15
OnlineITGuru

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How to use angle bracket with Function?:

We use angle brackets ” to specify parameter types in the generic function definition. Then to call the function, we just pass the expecter type as a parameter. We can also write generic functions that can be called with different types of arguments based on the type of arguments passed to the generic method, the compiler handles each method.

// To create a generic function
public static  void func(T a, T b){}

Note: In Parameter type,
      we can not use primitives like 
      'int', 'char' or 'double'.

// A Simple Java program 
// to show working of user defined 
// Generic functions 

class Test { 
	// A Generic method example 
	static <T> void genericDisplay(T element) 
	{ 
		System.out.println( 
			element 
				.getClass() 
				.getName() 
			+ " = " + element); 
	} 

	// Driver method 
	public static void main(String[] args) 
	{ 
		// Calling generic method 
		// with Integer argument 
		genericDisplay(11); 

		// Calling generic method 
		// with String argument 
		genericDisplay("OnlineITGuru"); 

		// Calling generic method 
		// with double argument 
		genericDisplay(1.0); 
	} 
} 

Output:

java.lang.Integer = 11
java.lang.String = GeeksForGeeks
java.lang.Double = 1.0

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