methods

Methods are subroutines that manipulate the data defined by the class and, in many cases, provide access to that data. In most cases, other parts of program will interact with a class through its methods.

In a well-written Java code, each method performs only one task.

main() is reserved for the method that begins execution of program.

ret-type name(parameter-list) 
{
	// body of method
}

• ret-type specifies the type of data returned by the method. This can be any valid type, including user defined class types. If the method does not return a value, its return type must be void.

• The parameter-list is a sequence of type and identifier pairs separated by commas.

• Parameters are essentially variables that receive the value of the arguments passed to the method when it is called. If the method has no parameters, the parameter list will be empty.

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class Vehicle
{
	int passengers;
	int fuelcap;
	int kpl;
	
	void range()
	{
		System.out.println("Range is " + fuelcap * kpl);
	} // no need of dot notation
}

class VehicleDemo
{
	public static void main(String[] args)
	{
		Vehicle minivan = new Vehicle();
		
		minivan.passengers = 7;
		minivan.fuelcap = 16;
		minivan.kpl = 21;
		
		System.out.print("Minivan can carry " 
			+ minivan.passengers + ". ");
		
		minivan.range(); // Displays range
	}
}

Minivan can carry 7. Range is 336

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Returning from a Method

return value; A non-void method must return a value by using this form of return.

NOTE

In a void method, immediate termination of a method can happen using return

class Vehicle
{
	int passengers;
	int fuelcap;
	int kpl;
	
	int range()
	{
		return fuelcap * kpl;
	} // no need of dot notation
}

class VehicleDemo
{
	public static void main(String[] args)
	{
		Vehicle minivan = new Vehicle();
		
		int range1;
		minivan.passengers = 7;
		minivan.fuelcap = 16;
		minivan.kpl = 21;
		
		range1 = minivan.range(); 
		// Displays range
		System.out.print("Minivan can carry " 
			+ minivan.passengers + "with range of " 
				+ range1 + " Miles.");
	}
}

Minivan can carry 7 with range of 336 Miles

Even range1 is not necessary as minivan.range() can be directly used in print.

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Using Parameters

Value passed to a method when it is called is an argument. Inside the method, the variable that receives the argument is called a parameter.

class CheckNum
{
	boolean isEven(int x)
	{
		if ( (x%2) == 0)
			return true;
		else 
			return false;
	}
}

class ParaDemo
{
	public static void main(String[] args)
	{
		CheckNum e = new CheckNum();
		
		if (e.isEven(10))
			System.out.println("10 is even");
		if(e.isEven(9))
			System.out.println("9 is even");
	}
}

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Multiple parameters

class Factor 
{
	boolean isFactor(int a, int b) 
	{
		if( (b % a) == 0) return true;
		else return false;
	}
}

class IsFact 
{
	public static void main(String[] args)
	{
		Factor x = new Factor();
		
		if(x.isFactor(2,20))
			System.out.prinln("2 is factor");
	}
}

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double fuelNeeded(int miles) 
{
	return (double) miles / mpg;
}

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