Java Tutorial – Method

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 teh console.

Now you will learn how to create your own methods with or without returning values, invokes a method with or without parameters, and apply method abstration ba batil in the program design.

Creating method:

Consider the following example to explain the syntax of a method:

public static int methodName(int a,int b)
{
//body, here goes the logic

}

here ,
public static: modifier
int : is return type
methodName: name of the method
a,b: formal parameters
int a,int b: list of parameters
method definition consists of a method header and a method body.The same is shown below:

modifier returnType nameOfTheMethod(parameter list)
{
//method body

}

modifier: it defines the access type of the method and it is optional to use.

returnType: method may return a value

nameOfTheMethod: This is the method name.The method signature consists of the method name and the parameter list.

Parameter List:The list of parameter 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 statements.

Example:

public static int minFunction(int n1,int n2)
{
int min;
if(n1>n2)
min=n2;
else
min=n1;
return min;
}

Method Calling:
– method returns a value
– returning nothing

example:

public class ExampleMinNumber {
	public static void main(String[] args){
		int a=11;
		int b=6;
		int c=minFunction(a,b);
		System.out.println("Minimum Value = "+c);
	}


public static int minFunction(int n1,int n2){
	int min;
	if(n1>n2)
		min=n2;
	else
		min=n1;
	return min;
	
}
}

method is the just like function in c/c++
output:

Minimum Value = 6

The void keyword:
The void keyword allows us to create methods which do not return a value.here in the void method methodRankPoints().This method is a void method which does not return any value.
example:

public class ExampleVoid {
	public static void main(String[] args){
		methodRankPoints(255.7);		
	}
	
	public static void methodRankPoints(double points)
	{
		if(points>=202.5)
		{
			System.out.println("Rank:A1");
		}
		else if(points>=122.4)
		{
			System.out.println("Rank: A2");
		}else
		{
			System.out.println("Rank:A3");
		}
	}
	
	
}

output:

Rank:A1

Passing Parameters by value:

public class SwappingExample {
public static void main(String[] args)
{
	int a=30;
	int b=45;
	
	System.out.println("Before swapping, a= "+a+" and b= "+b);
	
	//Invoke the swap method
	swapFunction(a,b);
	System.out.println("Now before and after swapping values will be");
	System.out.println("After swapping, a= "+a+" and b is "+b);
}

public static void swapFunction(int a,int b)
{
	System.out.println("Before swapping(Inside), a= "+a+" b= "+b);
	//
	int c;
	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
After swapping, a= 30 and b is 45

Method Overloading:
When a class has two or more methods by same name but different parameters, it is known as method overloading.It is different from overriding.In overriding a method has same method name,type,number of parameters etc.

example:

public class ExampleOverLoading {
public static void main(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 paramaters
	double result2=minFunction(c,d);
	System.out.println("Minimum value= "+result1);
	System.out.println("Minimum value= "+result2);
}
//for integer
public static int minFunction(int n1,int n2)
{
	int min;
{
	if(n1>n2)
		min=n2;
	else
		min=n1;
}
return min;
}
//for double
public static double minFunction(double n1,double n2)
{
	double min;
	if(n1>n2)
		min=n2;
	else
		min=n1;
	
	return min;
}

}

output:

Minimum value= 6
Minimum value= 7.3

Using Command Line Arguments:

Sometimes you need to pass command to a  program by command line arguments into main()

The Constructors:
Parametarized constructor:
Here is a simple example that uses a constructor with parameter:

public class MyClass {
int x;
//Following is the constructor
MyClass(int i)
{
	x=i;
}
}

You would call constructor to initialize objects as follows:

public class ConsDemo {
public static void main(String[] args)
{
MyClass t1=new MyClass(10);	
MyClass t2=new MyClass(20);
System.out.println(t1.x+" "+t2.x);	
}
}

output:

10 20

The this keyword:
this is a keyword in Java which is used as a reference to the object of the current class, with 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 name, within a constructor or a method.

class Student{
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.

Class Student{
int age;
Student()
{
this(20);
}
Student(int age)
{
this.age=age;
}

}

This এর ব্যাপারটা আরো ক্লিয়ার করতে হবে পরে

Variable Arguments(var-args)
typeName…parameterName

public class VarArgsDemo {
public static void main(String[] args)
{
	//Call method with variable args
	printMax(34,3,3,2,56.5);
	printMax(new double[]{1,2,3})
}

public static void printMax(double...numbers)
{
	if(numbers.length==0)
		System.out.println("No argument passed");
	return;
}

double result=numbers[0];
for(int )

}

there is another method finalize() method
syntax:

protected void finalize()
{
//finalization code here
}