If statement

This is used to get a decision in programming language. There are four basic types of "If statements". First we look at the structures of them and then try programs.

Structure 01

if ( condition )
{
   //statement executes when boolean condition is true
}

public class Apple {
 public static void main(String[] args) {

  int x = 12;

  if (x == 10) {
   System.out.print("X: " + x);
  }
 }
}

Structure 02

if ( condition )
{
     //statement executes when boolean condition is true
}
else
{
     //statement executes when boolean condition is false
}

public class Apple {
 public static void main(String[] args) {

  int x = 12;

  if (x == 10) {
   System.out.print("X: " + x);
  } else {
   System.out.print("X is invalid ");
  }
 }
}

Structure 03

if ( condition one )
{
     //statement executes when boolean condition one is true
}
else if(condition two )
{
     //statement executes when boolean condition two is true
}
else if(condition three )
{
     //statement executes when boolean condition three is true
}
else
{
     //statement executes when all boolean conditions are false
}

public class Apple {

 public static void main(String args[]) {

  int x = 85;

  if (x < 35) {
   System.out.println("Grade is F");
  }

  else if (x < 55) {
   System.out.println("Grade is C");
  }

  else if (x < 65) {
   System.out.println("Grade is B");
  }

  else if (x < 75) {
   System.out.println("Grade is A");
  }

  else {
   System.out.println("Grade is A+");
  }

 }
}

Structure 04

if( condition X )
{
     if(condition Y)
{
     //statement executes when boolean condition Y is true
}
else
{
//statement executes when boolean condition Y is false
}
}
else
{
     //statement executes when boolean condition X is false
}

public class Apple {
 public static void main(String[] args) {

  int x = 10;

  if (x == 10) {
   if (x < 5) {
    System.out.print("x < 5");
   } else {
    System.out.print("x > 5");
   }
  } else {
   System.out.print("X is invalid ");
  }
 }
}

You can use if-else without curly brackets.

public class Apple {

 public static void main(String args[]) {

  int x = 20;

  if (x != 10)
   System.out.println("X is not equal to 10");

  /*
   * if you don't add "{}" it will automatically add the brackets and
   * close the bracket after the first execution line
   */

 }
}

public class Apple {

 public static void main(String args[]) {

  int x = 20;

  if (x != 10)
   System.out.println("X is not equal to 10");
  /*
   * if you don't add "{}" it will automatically add the brackets and
   * close the bracket after the first execution line
   */
 }
}

public class Apple {

 public static void main(String args[]) {

  int x = 20;

  if (x != 10)
   ;
  else
   ;
  System.out.println("x == 10");

  /* This is legal but you can't add any other line between if and else */
 }
}