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Prasanth
Prasanth

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Java Methods

#java #programming #method

What is method?

  • Method is block of code or collection(group) of statement that perform a specific task.All method in java belong to a class.method similar to function and expose the behavior of objects.which only runs when it is called.
  • method must have return type weather void or return data like int , string...etc
  • Method Naming convention in java first letter should be lowercase verb and use camel case for multiple words.

Syntax

AccessModifer returntype methodName(Parameter List) { // method body }
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Access Modifiers:-

=> public, private, protected, default – controls method access

Method overloading:

Same class same method name , different parameters
(compile-time polymorphism)

Method Overriding:-

Different class (extend(is an-relationship) )parent and child relationship and Redefining-parent method in child class( same method name and parameters)

Types of methods:

In java is contain predefined and custom method , those methods have static and non-static method, we will see the later predefined methods(Already defined in the Java class libraries(Built-method)) .

 Object (java.lang.Object) ↑ Your Custom Class
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  • In java Object class have already told static method and non static method, that object class contain mostly non-static method that method public-ally accessible and static methods have private or package-private(default-both classes have same package not to be subclass). they are not accessible for normal java developers,most of them used Jvm internally.

Predefine Static methods:

Example:-

1.Math -> Math.pow(x, y) -> Power (x^y)
2.Arrays -> Arrays.sort(arr) -> Sorts an array
3.Collections -> Collections.sort(list) ->Sorts a list.

Redefine Non-Static methods:

1.String -> str.length() Returns string length
2.String -> str.toUpperCase() Converts to 3.uppercase -> Scanner scanner.nextInt() Reads an int from user input
4.ArrayList -> list.add(x) Adds element to list

  • Static method
  • Instance method
  • Construtor(special method)

Why use methods?

To reuse code: define the code once , and use it many times

without method

public class Test_Withoutmethod { public static void main(String[] args) { int a =5 , b=3; int sum = a+b; System.out.println("Sum: "+ sum); int x=10, y=2; int result =x*y; System.out.println("Sum: "+result); } }
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with method:

 public class Test_withMethod { static void add(int a , int b) { int sum =a+b; System.out.println("Sum: "+ sum); } public static int minFunction(int n1, int n2) { int min; // System.out.println("Min value is : "+min); you can not initialize local variable ,when printing came compile time error. if (n1>n2) { min =n2; System.out.println("Min:n2 is : "+min); return min; } else { min=n1; System.out.println("Min:n1 is : "+min); return min; } } public static void main(String[] args) { add(5,3);// callmethod add(10,2); // reuse method minFunction(1,2); } }
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Method Defining and Calling with return types and void :-

 // method defining and calling public class Method_Example1 { public static void main(String[] args) { int total= add(210,210); System.out.println(" Return value example => Total: 210+210 = "+total); twlethMark(550); } // method using to void example public static void twlethMark(int mark) { if(mark>580) { System.out.println("Rank:A1"); } else if (mark >=550) { System.out.println("Rank:A2"); } else { System.out.println("Rank:A3"); } } public static int add (int n1,int n2) { int total = n1+n2; return total; } }
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swapping values inside method:-

public class Method_SwappingValue {

public static void main(String[] args) { int a =30; int b =45; System.out.println("Before swapping, a =" +a+ " and b ="+b); swapValueinFunction(a,b); System.out.println("\n Now ,Before and After swapping values will be same here"); System.out.println("After swapping, a = "+a + ", b = "+b); }
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public static void swapValueinFunction(int a, int b) {
System.out.println("Before swapping(Inside), a = "+a + ", b = "+b);

int c =a; // a(30) value moved to c (),now a (empty) is empty a= b; // b(45) value moved a, because a is empty, now a is 45 b=c; // c(30) value moved to b(empty) , now b is 30 System.out.println("After swapping(Inside), a = "+a + ", b = "+b); }
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}

Method&Calling_Passing_Parameters

public class Method_Passing_Parameters { static String letter = " open the letter\n \n" + "To Smantatha,\n" + "\n" + "You are my heartbeat 💓\n" + "My heart is not beeping... because you're not near to hear it.\n" + "Come close and make it beep again.\n" + "Make my heart lovable with your presence. ❤️\n" + "\n" + "Forever yours,\n" + "Prasanth 💌"; public static void main(String[] args) { sendLetter("prasanth","Java Developer"); //passing string parameter } static void readLetter(String reader,String career,int age) { System.out.println(reader+" read the letter from prasanth:"); System.out.println(reader + letter); } static void sendLetter(String sender,String career) { System.out.println(sender+" sent a letter to samantha"); //System.out.println("Message: "+letter); System.out.println(); readLetter("samantha","Actress",35); } }
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Example: method using to return value and void 

public class JavaReturnandVoid{ public static void main(String[] args) { int Balance =myAccountBalance(100); System.out.println("Balance: "+Balance); System.out.println("\n"); samInfo(25,55); char [] data=samInfo(25,55,5.9); System.out.println(data); } static void samInfo(int i, int j) { System.out.println("Age: "+i); System.out.println("Weight: "+j); } // differen paremeter if you have , how to return ? static char[] samInfo(int i, int j, double d) { System.out.println("differen paremeter if you have ? how to return "); String data = "Age:" +i+", weight"+j+", Height:"+d; return data.toCharArray(); //convert to char[] } static int myAccountBalance(int AccountBalnce ) { int myPurse = 1; int Balance =myPurse+AccountBalnce; return Balance; } } <u>How to different way return the value:-</u>
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public class MethodReturnExample {

public static void main(String[] args) { // 1. calling void method greet(); // 2. calling int return method int sum=add(210,210); System.out.println("sum: "+ sum); //3.calling String return method String message=getMessage("Prasanth"); System.out.println(message); //4. calling method that returns both and string Object[] data=getUserinfo(); System.out.println("Id "+ data[0]); System.out.println("Name "+ data[1]); }
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// 1.void method - just print
static void greet() {
System.out.println("Hello ,Welcome to java ");
}
//2. return int

static int add(int num1,int num2)
{
int sum= num1+num2;
return sum;

}
//3. return string

static String getMessage(String name)
{
return "Hi My name is " + name +" i am Javadeveloper";
}

//4. return int and string using object[] or Array
static Object[] getUserinfo()
{
int id =101;
String name ="Hellow";
return new Object[] {id,name};
}

}

 <u> Important Return Type Scenarios</u>
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int return 5 + 3; Return a number
String return "Hello"; Return a message or text
boolean return a > b; Return true/false
char[] return name.toCharArray(); Return letters from a string
Array return new int[]{1,2,3}; Return multiple numbers
Object return new Person(...); Return class object
void System.out.println("Hi"); Just perform action, no return

 // method ovlerloading and overriding we will see Java Oops concept <u>Method&Block Scope:-</u>
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public class MethodandBlock_Scope_Example {

public static void main(String[] args) {
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//System.out.println(x);
int a =100;
System.out.println(a);
//method Scope: x is visible any where inside main method
//Anywhere in the method
int x =100;
System.out.println("x in method:"+x);

 if(x>50) { //Block Scope: y is only visible inside this if block //only inside the block int y =200; System.out.println("Y in if block: "+y); } // try to access y outside the block // System.out.println("y is outside if block: "+y); //error not visible out of block }
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}

 <u>Java Recursion:-</u>
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package java_Method;

// Factorial Using Recursion
public class Recursion_Example {

int fact(int n) { int result; if (n==1) return 1; result =fact(n-1) * n; /*fact(3-1) *3 -> fact (2) * 3 becomes -> (fact(1) *2)*3) * fact(4-1) *4 -> fact (3) * 3 * * * * */ return result ; } public static void main(String[] args) { Recursion_Example obj1 = new Recursion_Example(); System.out.println("Factorial of 3 is "+ obj1.fact(3)); System.out.println("Factorial of 4 is "+ obj1.fact(4)); System.out.println("Factorial of 5 is "+ obj1.fact(5));
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  • fact(5) = 5 x 4 x 3 x 2 x 1 =120
  • fact(1) = 1
  • fact(2) =1*2 =3
  • fact(3) =2*3 =6
  • fact(4) =6*4 = 24
  • fact(5) =24*5 =120
  • ------------------
  • fact(4) = 4 × 3 × 2 × 1 = 24
  • fact(1) =1
  • fact(2) =1*2 =3
  • fact(3) =2*3 =6
  • fact(4) =6*4 =24
  • fact(4) =24
  • ------------------
  • fact(3) = 3 × 2 × 1 = 6
  • fact(1) =1
  • fact(2) =1*2 =2
  • fact(3) =2*3 =6
  • ------------

  • *

    }

}
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// Sum of Natural Numbers Using Recursion
public class RecursionExample1 {

public static void main(String[] args) { int result = sum(10); System.out.println(result); } public static int sum(int k) { if(k>0) { return k+ sum(k-1); } else { return 0; } }
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}

 <u>Feature of Static Method:-</u> - A static Method in java manage to the class, not with object (or) instance. - It can be accessed by all instance of in the class, but it does not relay on specific instance. - static method can accessed directly static variable without need to create object ,you can access directly. but can not access non-static member directly you need to create to object. - you can call static method directly another static method and non-static method. <u>Features of Non-static Method:-</u> - In an instance method, you can access both instance and static members (field(use) and methods(calling) directly, without creating an object. -static variable can not declare to instance and non-static method is useless , you can use only class level not inside of methods. Types of instance Method:- 1.Accessor Method (Getters) Used to read/access the value of a private instance variable, start with the get.
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public class Person {
private String name; /private variable

//Accessor method (getter)
public String getName()
{
return name;
}

 2.Mutator methods (Setters) used to update/modify the value of private instance variable.Also supports encapsulation.start with set.
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public class person
private String name;

//Mutator method (setter)
public void setName(String name)
{
this.name =name;
}
{
this.name = name;
}
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