Methods(Methods)

Methods, Command Line Arguments, Aliasing and Recursion

Introduction Method is a part of class Contains particular set of instructions

One method in one class of program Main Method

Classes can contain many methods A method should perform a single well defined

task Two parts to be done in a program

Declare and Define a method Call a Method

Program jumps to execute instructions written in program and after executing them in sequential manner, comes back to the calling instruction

Introduction Have you ever invoke (call) a method?

Scanner sc = new Scanner(System.in);int x = sc.nextInt();

System.out.println(“Hello”);

Method definition

Method concept

Methods – Without Arguments

public class xyz{

public static void main(String[] args){

foo(); // Method call}static void foo() // Method definition{ // start of Method body

System.out.println("Hello World");// Method body

}// end of Method body}

Methods – With Arguments

public class xyz{

public static void main(String[] args){

int x;x=15;foo(x); // passing x as parameter

}static void foo(int a) // creating a alias of x{

System.out.println("value is: "+a); }

}

Methods – with multiple argumentspublic class xyz{

public static void main(String[] args){

int x = 15, y= 20;double z= 20.5;foo(x, y, z);

}static void foo(int a, int y, double c){

System.out.println("x or a: "+a);System.out.println("y: "+y);System.out.println("z or c:"+c);

}}

Methods with shared datapublic class xyz{

static int z= 20; // shared by all Methods of class xyzpublic static void main(String[] args){

int x;x=15;foo(x);System.out.println("Z=: "+z);

}static void foo(int a){

System.out.println("value is: "+a);System.out.println("value is: "+z);

}}

Methods – return Valuepublic class xyz{

public static void main(String[] args){

int x = 15, y= 20;int result = foo(x, y); //outcome is received in

variableSystem.out.println("result is: "+result);

}static int foo(int a, int b) // data type of return is

defined{

int sum;sum= a+b;return sum; // return a variable or value

}}

The type of the expression in the return statement must match the

return type in the Method header.

• Formal parameters are variables that are declared in the header of the Method definition.

• Actual parameters are the expressions in the calling statement.

• The formal and actual parameters must match exactly in type, order, and number. Their names, however, do not need to be the same.

It is the nature of the task to be performed, not the amount of code,

that determines if a Methodshould be used.

Variables are in scope from their point of definition until the end of their

Method or block.

ACCESSING Method Defined in some other class

CLASS A CLASS Bpublic class B{

public static void main(String[] args)

{ABC a1 = new ABC();a1.func1();

}}

class ABC{

static void func1(){

System.out.println(“hello”);}

}

class ABC{

static void func1(){

System.out.println("Hello");}

}public class xyz{

public static void main(String[] args){

ABC a1 = new ABC();a1.func1();

}

}

Command-Line Arguments

Command-Line Arguments A Java application can accept any number of

arguments from the command line. This allows the user to specify configuration

information when the application is launched. The user enters command-line arguments

when invoking the application and specifies them after the name of the class to be run

While running the program any things written after the name of the class are the command line arguments.

Arguments are delimited by the space.

String Command-Line Argumentspublic class Echo { public static void main (String[] args)

{ for (String s: args)

{ System.out.println(s);

} }}

javac Echo.javajava Echo Hello to the World

Output:

String Command-Line Argumentspublic class Echo {

public static void main (String[] args) {

for (int i=0; i<args.length; i++) {

System.out.println(args[i]); } }}

javac Echo.javajava Echo Hello to the World

Output:

Integer Command-Line Argumentspublic class Echo {

public static void main (String[] args) {

int argument;for (int i=0; i<args.length; i++) {

argument = Integer.parseInt(args[i]);System.out.println(argument);

} }}

javac Echo.java

Recursion

Factorial (3) recursively

Fibonacci numbers

Every recursive call must either solve part of the problem or reduce the size

of the problem.

Towers of Hanoi—start position

Towers solution for two disks

Towers solution for three disks

Towers solution for three disks (continued)

Recursive program of factorialpublic class recursive{

public static void main (String[] args) {

int n=5;int factorial=fact(n);System.out.println("factorial is: "+factorial);

}static int fact(int number){

if(number == 1){

return 1;}else{

return (number * fact(number-1));//self calling Methods

}}

}