Java - Methods

JAVA - METHODS



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A Java met hod is a collect ion of st at ement s t hat are grouped t oget her t o perform an operat ion. When you call t he Syst em.out .print ln met hod, for example, t he syst em act ually execut es several st at ement s in order t o display a message on t he console. Now you will learn how t o creat e your own met hods wit h or wit hout ret urn values, invoke a met hod wit h or wit hout paramet ers, overload met hods using t he same names, and apply met hod abst ract ion in t he program design.

Creat ing Met hod:

Considering t he following example t o explain t he synt ax of a met hod:

public static int funcName(int a, int b) { // body

}

Here, public static : modifier. int: ret urn t ype funcName: funct ion name a, b: formal paramet ers int a, int b: list of paramet ers

Met hods are also known as Procedures or Funct ions: Pro cedures: They don't ret urn any value. Functio ns: They ret urn value.

Met hod definit ion consist s of a met hod header and a met hod body. The same is shown below:

modifier returnType nameOfMethod (Parameter List) { // method body

}

The synt ax shown above includes: mo difier: It defines t he access t ype of t he met hod and it is opt ional t o use. returnT ype: Met hod may ret urn a value. nameOfMetho d: This is t he met hod name. The met hod signat ure consist s of t he met hod name and t he paramet er list . Parameter List: The list of paramet ers, it is t he t ype, order, and number of paramet ers of a met hod. These are opt ional, met hod may cont ain zero paramet ers. metho d bo dy: The met hod body defines what t he met hod does wit h st at ement s.

Example:

Here is t he source code of t he above defined met hod called max(). This met hod t akes t wo paramet ers num1 and num2 and ret urns t he maximum bet ween t he t wo:

/** the snippet returns the minimum between two numbers */ public static int minFunction(int n1, int n2) {

int min; if (n1 > n2)

min = n2; else

min = n1;

return min; }

Met hod Calling:

For using a met hod, it should be called. There are t wo ways in which a met hod is called i.e. met hod ret urns a value or ret urning not hing (no ret urn value).

The process of met hod calling is simple. When a program invokes a met hod, t he program cont rol get s t ransferred t o t he called met hod. This called met hod t hen ret urns cont rol t o t he caller in t wo condit ions, when:

ret urn st at ement is execut ed.

reaches t he met hod ending closing brace.

The met hods ret urning void is considered as call t o a st at ement . Let s consider an example:

System.out.println("This is !");

The met hod ret urning value can be underst ood by t he following example:

int result = sum(6, 9);

Example:

Following is t he example t o demonst rat e how t o define a met hod and how t o call it :

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);

}

/** returns the minimum of two numbers */ public static int minFunction(int n1, int n2) {

int min; if (n1 > n2)

min = n2; else

min = n1;

return min; } }

This would produce t he following result :

Minimum value = 6

The void Keyword:

The void keyword allows us t o creat e met hods which do not ret urn a value. Here, in t he following example we're considering a void met hod methodRankPoints. This met hod is a void met hod which does not ret urn any value. Call t o a void met hod must be a st at ement i.e. methodRankPoints(255.7);. It is a Java st at ement which ends wit h a semicolon as shown below.

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"); }

} }

This would produce t he following result :

Rank:A1

Passing Paramet ers by Value:

While working under calling process, argument s is t o be passed. These should be in t he same order as t heir respect ive paramet ers in t he met hod specificat ion. Paramet ers can be passed by value or by reference.

Passing Paramet ers by Value means calling a met hod wit h a paramet er. Through t his t he argument value is passed t o t he paramet er.

Example:

The following program shows an example of passing paramet er by value. The values of t he argument s remains t he same even aft er t he met hod invocat ion.

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("\n**Now, Before and After swapping values will be same here**:"); 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);

// Swap n1 with n2 int c = a; a = b; b = c;

System.out.println("After swapping(Inside), a = " + a + " b = " + b);

} }

This would produce t he following result :

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

Met hod Overloading:

When a class has t wo or more met hods by same name but different paramet ers, it is known as met hod overloading. It is different from overriding. In overriding a met hod has same met hod name, t ype, number of paramet ers et c.

Let s consider t he example shown before for finding minimum numbers of int eger t ype. If, let s say we want t o find minimum number of double t ype. Then t he concept of Overloading will be int roduced t o creat e t wo or more met hods wit h t he same name but different paramet ers.

The below example explains t he same:

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 parameters 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; } }

This would produce t he following result :

Minimum Value = 6 Minimum Value = 7.3

Overloading met hods makes program readable. Here, t wo met hods are given same name but wit h different paramet ers. The minimum number from int eger and double t ypes is t he result .

Using Command-Line Argument s:

Somet imes you will want t o pass informat ion int o a program when you run it . This is accomplished by passing command-line argument s t o main( ).

A command-line argument is t he informat ion t hat direct ly follows t he program's name on t he

command line when it is execut ed. To access t he command-line argument s inside a Java program is quit e easy.t hey are st ored as st rings in t he St ring array passed t o main( ).

Example:

The following program displays all of t he command-line argument s t hat it is called wit h:

public class CommandLine {

public static void main(String args[]){ for(int i=0; i ................
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