The Java if statement is used to test the condition. It checks boolean condition: true or false. There are various types of if statement in Java.

Some abbreviations that will be used in this learning:

System.out.print - SOP
System.out.println - SOPln

Code question

Check if someone has normal temperature: Normal temp = 98.0 to 98.9

98.1 -> Normal temperature
99 -> Not normal temperature
97.9 -> Not normal temperature

Explain -> 98.0________98.9_

96.8 -> Not normal temperature
98.5 -> Normal temperature

Scanner sc = new Scanner(System.in);
double temp = sc.nextDouble();
if (temp >= 98.0 && temp >= 98.9) {
    System.out.println("Normal temperature");
}

2. The else Statement

Now, we want to do something or the other accordingly when the condition is true or false. Use the else statement to specify a block of code to be executed if the condition is false.

Syntax of if....else

if (condition) {
    // Statements to run, when above condition True
} else {
    // Statements to run, when above condition False
}

Flow 1

if (condition) {
    Statement 1
} else {
    Statement 2
}

If Condition is True: Statement 1 will execute
If Condition is False: Statement 2 will execute

Flow 2

Statement 1
if (condition) {
    Statement 2
} else {
    Statement 3
}
Statement 4

If Condition is True: Statement 1, 2, 4 will execute
If Condition is False: Statement 1, 3, 4 will execute

Example 1: Read age of a person, check if person is at retirement age, or still have few years left to work. Retirement age is 65.

Scanner sc = new Scanner(System.in);
int age = sc.nextInt();
if (age > 65) {
    System.out.println("Retired");
} else {
    System.out.println("Few more years of service.");
}

Q1. Predict the output:

if (9 > 5) {
   System.out.println("If block");
} else {
   System.out.println("Else block");
}

If block
If block
Else block
Error

Q2. Predict the output:

Predict the output:

if (false) {
   System.out.println("Line 1");
} else {
   System.out.println("Line 2");
}

Line 1
Line 2
Line 1
Line 2
Error

Modulus Operator

Modulus operator (%) -> Gives remainder

System.out.println(17 % 4) -> Remainder = 1
System.out.println(24 % 2) -> Remainder = 0
System.out.println(97 % 2) -> Remainder = 1
System.out.println(82 % 2) -> Remainder = 0

Explain even and odd numbers.
Even numbers: Numbers which are divisible by 2.
Eg: 2, 4, 6, 8, 10, 12..
When we divide the number with 2, remainder = 0
Odd numbers: Numbers which are not divisible 2.
Eg: 1, 3, 5, 7, 9, 11..
When we divide the number with 2, remainder = 1

Example 1: Read a number and check if number is odd or even.

Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
if (a % 2 == 0) {
    System.out.println("Number is even");
} else {
    System.out.println("Number is odd");
}

Example 2: Check if a number is divisible by 5.

Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
if (a % 5 == 0) {
    System.out.println("Number is divisible by 5");
} else {
    System.out.println("Number is not divisible by 5");
}

Example 3: Check if a number is divisible by 2 or 3.

Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
if (a % 2 == 0 || a % 3 == 0) {
    System.out.println("Number is divisible by 2 or 3");
} else {
    System.out.println("Number is not divisible by 2 and 3 both");
}

Question: Can we have if without an else block?

Yup!!
Nope!!
Don't know

Question: Can we have else without an if block?

Choices

Yup!!
Nooo!!
Maybe

Code Question's (Assignment)

Question: Read 2 numbers and print max of 2 numbers.

Examples:

a = 5 , b = 10
Max of a and b = 10

a = 15 , b = 10
Max of a and b = 15

Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
int b = sc.nextInt();
if (a > b) {
    System.out.println(a);
} else {
    System.out.println(b);
}

Question: Predict the output: For input: 45 45

Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
int b = sc.nextInt();
if (a > b) {
    System.out.print(a);
} else {
    System.out.print(b);
}

Choices

Error
45
45
45

10 Question: Categorize Number
Given an integer n0, categorize it into positive, negative or zero.

Category:

n = 10: n > 0: print "positive number"
n = -27: n < 0: print "negative number"
n = 0: n == 0: print "zero"

public static void main() {
    Scanner sc = new Scanner(System.in);
    int a = scn.nextInt();
    if (a > 0) {
        System.out.println("positive number");
    }
    if (a < 0) {
        System.out.println("negative number");
    }
    if (a == 0) {
        System.out.println("zero");
    }
}

Syntax:

if (cond_1) {
    // Statements if cond_1 is true
} else if (cond_2) {
    // Statements if cond_1 is false and cond_2 is true
} else {
    // Statements if cond_1 is false and cond_2 is false
}

Note: "else" is optional.

3. The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Flow

Statement 1
if (cond_1) {
    // block of code to be executed if condition1 is true
    Statement 2
} else if (cond_2) {
    // block of code to be executed if the condition1 is false and condition2 is true
    Statement 3
} else {
    // block of code to be executed if the condition1 is false and condition2 is false
    Statement 4
}
Statement 5

Explain the above flow according to below table.

Conditions which are true	Statements executed
1	1 2 5
2	1 3 5
All false	1 4 5
1 2	1 2 4

Note: If a condition is true, it will execute and will come out of If/Else block and execute remaining statements.
Note: We can have multiple "else if ()" blocks.

Back to Categorize number problem,

public static void main() {
    Scanner sc = new Scanner(System.in);
    int a = scn.nextInt();
    if (a > 0) {
        System.out.println("positive number");
    } else if (a < 0) {
        System.out.println("negative number");
    } else {
        System.out.println("zero");
    }
}

Example: Is the below code correct or not?

int a = 10;
else if (a > 5) {
    System.out.println("Number is more than 5");
} else {
    System.out.println("Number is not more than 5");
}

Correct Answer: Compilation error.

We cannot write any else if () without if () block.

Question: What will be the output of the following:

if (true) {
    System.out.println("1");
} else if (true) {
    System.out.println("2");
} else if (true) {
    System.out.println("3");
}

1
1
2
3
2
3

Question: Can there be an else if block without a if block

Yes
No
Maybe

Question: Can there be an else if block without an else block

Yes
No
Maybe

Question: What will be the output of the following code?

int a = 10,b = 10;
if (a >= 10 && b >= 10) {
   System.out.print(a+b);
}

10
20
30
None

Question: What will be the output of the following code?

int a = 10;
int b = 10;
if ( ++ a >= 12 && ++ b >= 12 ) {
  System.out.println("Hello");
}
System.out.println(a + b);

Hello
10
22
21
None

Question: What will be the output of the following code?

int a = 10;
int b = 10;
if ( ++ a >= 11 || ++ b >= 12 ) {
  System.out.println("Hello");
}
System.out.println(a + b)

20
22
Hello
21
None

Question: What will be the output of the following code?

int a = 10;
int b = 10;
if ( ++ a >= 12 || ++ b >= 12 ) {
  System.out.println("Hello");
}
System.out.println(a + b);

20
21
22
None

Question: What will be the output of the following code?

int N = 5;
if (N > 2)
    System.out.println("Yayay");
else
    System.out.println("Blahblah!!");

Yayay
Blahblah!!

Question: What will be the output of the following code?

int N = 5;
if (N > 2)
    System.out.println("Yayay");
    System.out.println("Hmmmm");
else
    System.out.println("Blahblah!!");
    System.out.println("Blahblah!!");

Error :(
No Error, this code rocks!
Yayay Hmmmm
Blahblah!!

Question: What will be the output of the following code?

int marks = 80; 
if (marks > 70) {
    System.out.print("Distinction "); 
    System.out.print("Congrats ");
} else if (marks > 35) { 
    System.out.print("Pass "); 
} else 
    System.out.print("Fail "); 
System.out.print("Good luck");

Distinction Congrats Good luck
Good luck
Error
Distinction Congrats

5. Categorize Triangles

Categorize Triangles : Categorize triangle on the basis of the length of the sides

Equilateral: When the length of the all the sides are equal.
Isosceles: When the length of any two sides are equal.
Scalene: When the length of all sides are different.

Let a, b, c be the length of the three sides of a triangle. Given in each case they take some values, tell the category of the triangle. It is the given that the input values for a, b, c are positive integer values.

a = 20, b = 20, c = 20 
-- Output = Equilaterial

a = 7, b = 12, c = 9 
-- Output = Scalene

a = 5, b = 13, c = 5 
-- Output = Isosceles

a = 12, b = 7, c = 7 
-- Output = Isosceles

The equivalent code for implementing the above logic is as follows:

if (a == b && b == c) {
   SOPln("Equilateral"); 
} else if (a == b || b == c || a == c) {
    SOPln("Isosceles");
} else {
    SOPln("Scalene");
}

6. Max of three: Given three numbers, print the maximum among them.

Note that a, b, c can take any integer values. Stress on the point that a, b, c can also take equal values. The three test case demonstrates this point.

* a = 7,  b = 20, c = 50 ==> max = 50
* a = 10, b = 9,  c = 10 ==> max = 10
* a = 3,  b = 3,  c = 3  ==> max = 3

The equivalent code for implementing the above logic is as follows:

if (a >= b && a >= c) {
   SOPln("a"); 
} else if (b >= c) {
    SOPln("b");
} else {
    SOPln("c");
}

7. Fizz-Buzz

Given a number, 
* print "Fizz" if the number is divisible by 3.
* print "Buzz" if the number is divisible by 5.
* print "Fizz-Buzz" if the number is divisble by both 3 and 5.

For example,

n = 39, O/p = Fizz
n = 25, O/p = Buzz
n = 15, O/p = Fizz-Buzz
n = 13, O/p = No output

How to implement this?

The following code shows a wrong implementation of the above logic:

if (n % 3 == 0) {
    SOPln("Fizz");
} else if (n % 5 == 0) {
    SOPln("Buzz");
} else {
    SOPln("Fizz-Buzz");
}

The above code prints "Fizz-Buzz" for n = 11, but this is wrong as n is neither divisble by 3 nor 5. So there should have no output for this number.

Another wrong implementation is as follows:

if (n % 3 == 0) {
    SOPln("Fizz");
} else if (n % 5 == 0) {
    SOPln("Buzz");
} else if (n % 3 == 0 && n % 5 == 0) {
    SOPln("Fizz-Buzz");
}

The above code prints "Fizz" for n = 15, but this is wrong as n is divisble by 3 and 5 both. So the correct output should be "Fizz-Buzz".

So finally, the correct implementation of this logic is as follows:

if (n % 3 == 0 && n % 5 == 0) {
    SOPln("Fizz-Buzz");
} else if (n % 3 == 0) {
    SOPln("Fizz");
} else if (n % 5 == 0) {
    SOPln("Buzz");
}

9. Nested If Else

Syntax:

Statement 1
if (cond1) {
    Statement 2
    if (cond2) {
        Statement 3
    } else {
        Statement 4
    }
    Statement 5
} else {
    Statement 6
    if (cond3) {
        Statement 7
    } else {
        Statement 8
    }
    Statement 9
}

Question: Predict the output of the following code?

int a = 10, b = 15;
if (a > 8) {
    if (a < b || b == 9) {
        System.out.println("Hi");
    } else {
        System.out.println("Bye");
    }
} else {
    System.out.println("Good Bye");
}

Hi
Bye
Good Bye
None

Question: Predict the output of the following code?

int a = 10, b = 15;
if (a > 8) {
    if (a == b || b < a) {
        System.out.println("Hi");
    }
    else {
        System.out.println("Bye");
    }
} else {
    System.out.println("Got it");
}

Hi
Bye
Got it
None

Question: Predict the output of the following code?

if (true) {
   if (true) {
       if (false) {
           System.out.println("Hey there");
       }
   }
   else {
       System.out.println("Hello");
   }
} else {
   System.out.println(10 / 0);
}

Hey there
Hello
No output
Error

Explanation: We are not getting an error because the inner if statement with the false condition is not executed due to the if condition being false. Therefore, the else block following it is also not executed. The program simply moves on to the next line, which is outside of any control structures and executes the statement System.out.println("Hello"); as expected.

The else block following the outer if statement is also not executed since the condition of the outer if statement is true, and the program again moves to the next line and executes the statement System.out.println("Hello");

Categorise the number Given a number, classify it as follows:

* +ve and even
* +ve and odd
* -ve and even
* -ve and odd

public static void main() {
    Scanner scn = new Scanner(System.in);
    int n = scn.nextInt();
    if (num > 0) {
        if (num % 2 == 0) {
            SOPln("Positive and even");
        }
        else {
            SOPln("Positive and odd");
        }
    }
    else {
        if (num % 2 == 0) {
            SOPln("Negative and even");
        }
        else {
            SOPln("Negative and odd");
        }   
    }
}

Scope of a Variable

It defines the point till where you can use the variable. You can only use a variable till the closing bracket of the block in which it was created.

Example 1:

public static void main() {
        
        
    int x;
    x = 5;

    int y;
    y = 20

}

Scope of variable x: Line 4 to 10 Scope of variable y: Line 7 to 10

Example 2:

public static void main() {
          
    int x = 10;
    if (x == 10) {
        int y = 5;
        SOP(y);
    }
    int z = 9;

}

Scope of variable x: Line 3 to 10 Scope of variable y: Line 5 to 7 Scope of variable z: Line 8 to 10

Example 3:

public static void main() {
    int a = 10;
    {
        a = 20;
    }
    SOP(a); 

}

Scope of variable a: Line 2 to 8 Also the code will print 20 as the changes done in the variable values are not restricted to that block in which the change is done. But the life of the variable is restricted to the block in which it was created.

Example 4:

public static void main() {
    int x = 10;
    {
        int y = 20;
        SOP(x + " " + y);
    }
    {
        SOP(x + " " + y); // This line will give error as y is not present in its scope
    } 

}

Example 5: Redefining variable error

public static void main() {
    int a = 90;
    {
        int a = 7; // This line will give error as variable a is already defined in this scope
        SOPln(a);
    }

}

Question: Predict the output of the following code:

public static void main(String args[]) {
    int x = 10;
    {
        int y = 20;
        System.out.println(x + " " + y);
    }
    {
        System.out.println(x + " " + y);
    }
    System.out.println(x + " " + y);
}

Error
10 20
10 20
10 20
10 20 10 20 10 20

Question: Predict the output of the following code:

public static void main() {
    int x = 10, y = 20;
    {
        SOP(x + " " + y);
    }
    {
        x = 15;
        SOPln(x + " " + y);
    }
    SOPln(x + " " + y);
}

10 20
15 20
10 20
Error
10 20
15 20
15 20
inky pinky ponky

Question: Predict the output of the following code:

if (true) {
    int x = 10;
    SOPln("Value of x is " + x);
    x ++ ;
}
SOPln("Value of x is " + x);

Value of x is 10
Value of x is 11
Value of x is 10
Value of x is 0
Value of x is 10
Value of x is 10
Error

Question: Predict the output of the following code:

int a = 0;
{
    int b = 10;
    SOPln("b = " + b);300
    int c = a + b;
    SOPln("c = " + c);
}
a = c + b; 
SOPln("a = " + a);

a = 20
b = 10
c = 10
b = 10
c = 10
a = 20
Error

Explanation: Error b and c are out of the scope

Question: Predict the output of the following code:

int a = 10, b = 5;
if (true) {
    int c = a * b;
}
SOPln(c);

50
Error
Need Coffee!!

Explanation: Error the variable c is out of the scope

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3. if-else in JAVA

Choices

Choices

Rahul Aher