Java Methods
A Java method is a collection of statements that are grouped together to perform an operation. When you call the System.out.println() method, for example, the system actually executes several statements in order to display a message on the console.
In this tutorial, we will learn how to create your own methods with or without return values, invoke a method with or without parameters, and apply method abstraction in the program design.
Creating a Java Method
To create a Java method, there should be an access modifier followed by the return type, method’s name, and parameters list.
Syntax to Create a Java Method
Considering the following example to explain the syntax of a method −
modifier returnType nameOfMethod (ParameterList){// method body}The syntax shown above includes −
- modifier − It defines the access type of the method and it is optional to use.
- returnType − Method may return a value.
- nameOfMethod − This is the method name. The method signature consists of the method name and the parameter list.
- Parameter List − The list of parameters, it is the type, order, and number of parameters of a method. These are optional, method may contain zero parameters.
- method body − The method body defines what the method does with the statements.
Example to Create a Java Method
Here is the source code of the above defined method called minFunction(). This method takes two parameters n1 and n2 and returns the minimum between the two −
/** the snippet returns the minimum between two numbers */publicstaticintminFunction(int n1,int n2){int min;if(n1 > n2)
min = n2;else
min = n1;return min;}Calling a Java Method
For using a method, it should be called. There are two ways in which a method is called i.e., method returns a value or returning nothing (no return value).
The process of method calling is simple. When a program invokes a method, the program control gets transferred to the called method. This called method then returns control to the caller in two conditions, when −
- the return statement is executed.
- it reaches the method ending closing brace.
The methods returning void is considered as call to a statement. Lets consider an example −
System.out.println("This is tutorialspoint.com!");The method returning value can be understood by the following example −
int result =sum(6,9);Example: Defining and Calling a Java Method
Following is the example to demonstrate how to define a method and how to call it −
publicclassExampleMinNumber{publicstaticvoidmain(String[] args){int a =11;int b =6;int c =minFunction(a, b);System.out.println("Minimum Value = "+ c);}/** returns the minimum of two numbers */publicstaticintminFunction(int n1,int n2){int min;if(n1 > n2)
min = n2;else
min = n1;return min;}}Output
Minimum value = 6
The void Keyword with Java Methods
The void keyword allows us to create methods which do not return a value. Here, in the following example we’re considering a void method methodRankPoints. This method is a void method, which does not return any value. Call to a void method must be a statement i.e. methodRankPoints(255.7);. It is a Java statement which ends with a semicolon as shown in the following example.
Example: Use of void keyword with Methods
publicclassExampleVoid{publicstaticvoidmain(String[] args){methodRankPoints(255.7);}publicstaticvoidmethodRankPoints(double points){if(points >=202.5){System.out.println("Rank:A1");}elseif(points >=122.4){System.out.println("Rank:A2");}else{System.out.println("Rank:A3");}}}Output
Rank:A1
Passing Parameters by Value in Java Methods
While working under calling process, arguments is to be passed. These should be in the same order as their respective parameters in the method specification. Parameters can be passed by value or by reference.
Passing Parameters by Value means calling a method with a parameter. Through this, the argument value is passed to the parameter.
Example: Passing Parameters by Value
The following program shows an example of passing parameter by value. The values of the arguments remains the same even after the method invocation.
publicclass swappingExample {publicstaticvoidmain(String[] args){int a =30;int b =45;System.out.println("Before swapping, a = "+ a +" and b = "+ b);// Invoke the swap methodswapFunction(a, b);System.out.println("\n**Now, Before and After swapping values will be same here**:");System.out.println("After swapping, a = "+ a +" and b is "+ b);}publicstaticvoidswapFunction(int a,int b){System.out.println("Before swapping(Inside), a = "+ a +" b = "+ b);// Swap n1 with n2int c = a;
a = b;
b = c;System.out.println("After swapping(Inside), a = "+ a +" b = "+ b);}}Output
Before swapping, a = 30 and b = 45
Before swapping(Inside), a = 30 b = 45
After swapping(Inside), a = 45 b = 30
**Now, Before and After swapping values will be same here**:
After swapping, a = 30 and b is 45
Java Methods Overloading
When a class has two or more methods by the same name but different parameters, it is known as method overloading. It is different from overriding. In overriding, a method has the same method name, type, number of parameters, etc.
Let’s consider the example discussed earlier for finding minimum numbers of integer type. If, let’s say we want to find the minimum number of double type. Then the concept of overloading will be introduced to create two or more methods with the same name but different parameters.
The following example explains the same −
Example: Methods Overloading in Java
publicclassExampleOverloading{publicstaticvoidmain(String[] args){int a =11;int b =6;double c =7.3;double d =9.4;int result1 =minFunction(a, b);// same function name with different parametersdouble result2 =minFunction(c, d);System.out.println("Minimum Value = "+ result1);System.out.println("Minimum Value = "+ result2);}// for integerpublicstaticintminFunction(int n1,int n2){int min;if(n1 > n2)
min = n2;else
min = n1;return min;}// for doublepublicstaticdoubleminFunction(double n1,double n2){double min;if(n1 > n2)
min = n2;else
min = n1;return min;}}Output
Minimum Value = 6
Minimum Value = 7.3
Overloading methods makes program readable. Here, two methods are given by the same name but with different parameters. The minimum number from integer and double types is the result.
Using Command-Line Arguments
Sometimes you will want to pass some information into a program when you run it. This is accomplished by passing command-line arguments to main( ).
A command-line argument is the information that directly follows the program’s name on the command line when it is executed. To access the command-line arguments inside a Java program is quite easy. They are stored as strings in the String array passed to main( ).
Example
The following program displays all of the command-line arguments that it is called with −
publicclassCommandLine{publicstaticvoidmain(String args[]){for(int i =0; i<args.length; i++){System.out.println("args["+ i +"]: "+ args[i]);}}}Try executing this program as shown here −
$java CommandLine this is a command line 200 -100
Output
args[0]: this
args[1]: is
args[2]: a
args[3]: command
args[4]: line
args[5]: 200
args[6]: -100
The this Keyword inside Java Methods
this is a keyword in Java which is used as a reference to the object of the current class, with in an instance method or a constructor. Using this you can refer the members of a class such as constructors, variables and methods.
Note − The keyword this is used only within instance methods or constructors
In general, the keyword this is used to −
- Differentiate the instance variables from local variables if they have same names, within a constructor or a method.
classStudent{int age;Student(int age){this.age = age;}}- Call one type of constructor (parametrized constructor or default) from other in a class. It is known as explicit constructor invocation.
classStudent{int age
Student(){this(20);}Student(int age){this.age = age;}}Example: Use of this keyword in Java Methods
Here is an example that uses this keyword to access the members of a class. Copy and paste the following program in a file with the name, This_Example.java.
publicclassThis_Example{// Instance variable numint num =10;This_Example(){System.out.println("This is an example program on keyword this");}This_Example(int num){// Invoking the default constructorthis();// Assigning the local variable <i>num</i> to the instance variable <i>num</i>this.num = num;}publicvoidgreet(){System.out.println("Hi Welcome to Tutorialspoint");}publicvoidprint(){// Local variable numint num =20;// Printing the local variableSystem.out.println("value of local variable num is : "+num);// Printing the instance variableSystem.out.println("value of instance variable num is : "+this.num);// Invoking the greet method of a classthis.greet();}publicstaticvoidmain(String[] args){// Instantiating the classThis_Example obj1 =newThis_Example();// Invoking the print method
obj1.print();// Passing a new value to the num variable through parametrized constructorThis_Example obj2 =newThis_Example(30);// Invoking the print method again
obj2.print();}}Output
This is an example program on keyword this
value of local variable num is : 20
value of instance variable num is : 10
Hi Welcome to Tutorialspoint
This is an example program on keyword this
value of local variable num is : 20
value of instance variable num is : 30
Hi Welcome to Tutorialspoint
Java Methods Variables Arguments (var-args)
JDK 1.5 enables you to pass a variable number of arguments of the same type to a method. The parameter in the method is declared as follows −
typeName... parameterName
In the method declaration, you specify the type followed by an ellipsis (…). Only one variable-length parameter may be specified in a method, and this parameter must be the last parameter. Any regular parameters must precede it.
Example: Use of Variables Arguments (var-args)
publicclassVarargsDemo{publicstaticvoidmain(String args[]){// Call method with variable args printMax(34,3,3,2,56.5);printMax(newdouble[]{1,2,3});}publicstaticvoidprintMax(double... numbers){if(numbers.length ==0){System.out.println("No argument passed");return;}double result = numbers[0];for(int i =1; i < numbers.length; i++)if(numbers[i]> result)
result = numbers[i];System.out.println("The max value is "+ result);}}Output
The max value is 56.5
The max value is 3.0
The finalize( ) Method
It is possible to define a method that will be called just before an object’s final destruction by the garbage collector. This method is called finalize( ), and it can be used to ensure that an object terminates cleanly.
For example, you might use finalize( ) to make sure that an open file owned by that object is closed.
To add a finalizer to a class, you simply define the finalize( ) method. The Java runtime calls that method whenever it is about to recycle an object of that class.
Inside the finalize( ) method, you will specify those actions that must be performed before an object is destroyed.
The finalize( ) method has this general form −
protectedvoidfinalize(){// finalization code here}Here, the keyword protected is a specifier that prevents access to finalize( ) by code defined outside its class.
This means that you cannot know when or even if finalize( ) will be executed. For example, if your program ends before garbage collection occurs, finalize( ) will not execute.
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