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Control Statements in Java

 

A control statement in Java is used to control the flow of execution of a program.
It allows the program to make decisions, repeat tasks, or jump to specific parts of code based on certain conditions.

There are three main types of control statements in Java:

1.      Decision-Making Statements

2.      Looping (Iteration) Statements

3.      Jump Statements

 

 Decision-Making Statements

Decision-making statements allow a program to choose which block of code to execute based on a condition.

Types of Decision-Making Statements:

1.      if statement

2.      if-else statement

3.      if-else-if ladder

4.      nested if statement

5.      switch statement

 

 Simple if Statement

·         The if statement checks a condition.

·         If the condition is true, the block of code inside the if is executed.

·         If it is false, the code is skipped.

Syntax:

if (condition) {
    // code to execute if condition is true
}

Example:

public class Student {
    public static void main(String[] args) {
        int x = 1;
        int y = 12;
 
        if (x + y > 20) {
            System.out.println("x + y is greater than 20");
        }
    }
}

Output:

x + y is greater than 20

 

 if-else Statement

·         The else block executes when the if condition is false.

Syntax:

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

Example:

public class Student {
    public static void main(String[] args) {
        int x = 10;
        int y = 12;
 
        if (x + y < 10) {
            System.out.println("x + y is less than 10");
        } else {
            System.out.println("x + y is greater than 20");
        }
    }
}

Output:

x + y is greater than 20

 

 if-else-if Ladder

·         Used when there are multiple conditions to check.

·         Only the first true condition’s block will execute.

Syntax:

if (condition1) {
    // executes when condition1 is true
} else if (condition2) {
    // executes when condition2 is true
} else {
    // executes when all conditions are false
}

Example:

public class Student {
    public static void main(String[] args) {
        String city = "Kathmandu";
 
        if (city == "Pokhara") {
            System.out.println("City is Pokhara");
        } else if (city == "Kathmandu") {
            System.out.println("City is Kathmandu");
        } else if (city == "Butwal") {
            System.out.println("City is Butwal");
        } else {
            System.out.println(city);
        }
    }
}

Output:

City is Kathmandu

 

 Nested if Statement

·         A nested if means an if statement inside another if or else block.

Syntax:

if (condition1) {
    if (condition2) {
        // executes when both are true
    } else {
        // executes when condition2 is false
    }
}

Example:

public class ElseIf {
    public static void main(String[] args) {
        String dist = "Rup";
        String village = "boadgaun";
 
        if (dist == "Kapilvastu") {
            System.out.println("District is Kapilvastu");
            if (village == "boadgaun") {
                System.out.println("Village is boadgaun");
            } else {
                System.out.println("Village is not inside Kapilvastu");
            }
        } else {
            System.out.println("District is not Kapilvastu");
        }
    }
}

 

 Switch Statement

·         Used when we have multiple options for a single variable.

·         It is easier than writing many if-else statements.

Syntax:

switch (expression) {
    case value1:
        // statements
        break;
    case value2:
        // statements
        break;
    ...
    default:
        // default statements
}

Example:

class Weekdays {
    public static void main(String args[]) {
        int day = 8;
 
        switch (day) {
            case 1: System.out.println("Sunday"); break;
            case 2: System.out.println("Monday"); break;
            case 3: System.out.println("Tuesday"); break;
            case 4: System.out.println("Wednesday"); break;
            case 5: System.out.println("Thursday"); break;
            case 6: System.out.println("Friday"); break;
            case 7: System.out.println("Saturday"); break;
            default: System.out.println("Wrong Choice! Enter 1 to 7 only");
        }
    }
}

Output:

Wrong Choice! Enter 1 to 7 only

 

 Looping (Iteration) Statements

Loop statements are used to execute a block of code repeatedly while a condition remains true.

Types of loops:

1.      for loop

2.      for-each loop

3.      while loop

4.      do-while loop

 

 for Loop

·         Used when we know how many times to repeat a block of code.

·         Combines initialization, condition, and increment/decrement in one line.

Syntax:

for (initialization; condition; increment/decrement) {
    // statements
}

Example:

public class Calculation {
    public static void main(String[] args) {
        int sum = 0;
        for (int j = 1; j <= 10; j++) {
            sum = sum + j;
        }
        System.out.println("The sum of first 10 natural numbers is " + sum);
    }
}

Output:

The sum of first 10 natural numbers is 55

 

 for-each Loop

·         Used to iterate through arrays or collections easily.

·         We don’t need to use indexes.

Syntax:

for (data_type var : array_name) {
    // statements
}

Example:

public class Calculation {
    public static void main(String[] args) {
        String[] names = {"Java", "C", "C++", "Python", "JavaScript"};
 
        System.out.println("Printing the contents of the array:");
        for (String name : names) {
            System.out.println(name);
        }
    }
}

Output:

Java
C
C++
Python
JavaScript

 

 while Loop

·         Used when we don’t know how many times to run the loop.

·         It checks the condition before executing the loop body.

Syntax:

while (condition) {
    // statements
}

Example:

public class Calculation {
    public static void main(String[] args) {
        int i = 0;
        System.out.println("Printing first 10 even numbers:");
        while (i <= 10) {
            System.out.println(i);
            i = i + 2;
        }
    }
}

Output:

0
2
4
6
8
10

 

 do-while Loop

·         Similar to the while loop, but it executes the loop at least once before checking the condition.

·         It is known as an exit-controlled loop.

Syntax:

do {
    // statements
} while (condition);

Example:

public class Calculation {
    public static void main(String[] args) {
        int i = 0;
        System.out.println("Printing first 10 even numbers:");
        do {
            System.out.println(i);
            i = i + 2;
        } while (i <= 10);
    }
}

Output:

0
2
4
6
8
10

 

3. Jump Statements

Jump statements are used to transfer control from one part of the program to another.

Types of Jump Statements:

1.      break statement

2.      continue statement

 

 break Statement

·         It terminates the current loop or switch statement.

·         The control moves to the next statement after the loop/switch.

Example:

public class BreakExample {
    public static void main(String[] args) {
        for (int i = 0; i <= 10; i++) {
            System.out.println(i);
            if (i == 6) {
                break;
            }
        }
    }
}

Output:

0
1
2
3
4
5
6

 

 continue Statement

·         It skips the current iteration and jumps to the next iteration of the loop.

Example:

public class ContinueExample {
    public static void main(String[] args) {
        for (int i = 0; i <= 2; i++) {
                if (i == 4) {
                    continue;
                }
                System.out.println(i);
            
        }
    }
}

Output:

0
1
2
3
5

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