Basic

Myth

• file name should be same as class name
• it should be same when class is public

// file name Main.java 
class ForGeeks {
 public static void main(String[] args)
 {
  System.out.println("For Geeks class");
 }
}

class GeeksTest {
 public static void main(String[] args)
 {
  System.out.println("Geeks Test class");
 }
}

this program will create who different classes ForGeeks.class GeeksTest.class

Variables & datatypes

• String
• int
• float
• boolean

• char

• final -constant read only

int a,b,c;
a=b=c=1;

String methods

https://www.w3schools.com/java/java_ref_string.asp

String x = "10";
int y = 20;
System.out.println(x+y); //1020

Math methods

• math methods are static

https://www.w3schools.com/java/java_ref_math.asp

Method overloading

• compile time polymorphism / Static Polymorphism/Early binding
• same name with:
• change in datatype of perimeter
• change in number of perimeter
• change in order of perimeter

Static and Public

• static method/attribute can be accessed without object
• public method/attribute can be accessed with object.

Modifier

• access modifiers
• provide access level
• classes: either public or default

• attribute, methods :public, private, protected, default

• default - The class is only accessible by classes in the same package

• protected: The code is accessible in the same package and subclasses.

• non-access modifiers

final class - can't be inherited
abstract class - can't be used to create object , must be inherited

attribute or methods

• final: can't be modified
• static: att. & method belong to class
• abstract - attribute defined inside abstract class applied only on methods

Encapsulation

• making attribute private

Packages

https://docs.oracle.com/javase/8/docs/api/

Build In

syntax

//import specific class
import package.name.Class;

//import whole package
import package.name.*;

example

import java.util.Scanner;

class ForGeeks {
 public static void main(String[] args)
 {
  System.out.println("For Geeks class");
 }
}

class GeeksTest {
 public static void main(String[] args)
 {
  try (Scanner myObj = new Scanner(System.in)) {
   System.out.println("Enter username");

   String userName = myObj.nextLine();
   System.out.println("Username is: " + userName);
  }

 }
}

User Define

// define your package name
package mypack;
import java.util.Scanner;

public class Basic {
    public static void main(String[] args) {
        try (Scanner obj = new Scanner(System.in)) {
            System.out.println("Enter surname");
            String surname = obj.nextLine();
            System.out.print(surname);
        }
    }
}

javac .\Basic.java
javac -d . .\Basic.java
java mypack.Basic