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Conditional Control Statements

  • Conditional Control Statements are also called as decision-making statements or selection statements.
  • It allows the program to select between alternative actions during the program execution.
  • The execution will be based on the result of conditional expression.

9.1.1 if Statement

1. Simple If​

if (condition) {
// Statements (IF BLOCK)
}

// Other Statements
It indicates whether IF BLOCK statements will be executed or not, as per the condition.

2. If-else Statement​

if (condition) {
// Statements (IF BLOCK)
}else {
// Statements (ELSE BLOCK)
}
  • It indicates which block will be executed based on the condition.
  • If condition is true, IF block executes.
  • Otherwise, ELSE block executes.

3. If Else-if Statement​

if (condition1) {
// Statements (Block 1)
}elseif (condition2) {
// Statements (Block 2)
}elseif (condition3) {
// Statements (Block 3)
}
...
else {
// Statements
}

Important Points​

  • Condition can be any expression that returns a boolean value.
  • Block notation {} is mandatory when there are multiple statements.
  • Block notation is optional when there is only one statement.
  • Variables declared inside an if or else block are local to that block only and cannot be accessed outside.

Lab161.java​

class Lab161 {

  public static void main(String[] args) {
    if (true) System.out.println("IF BLOCK");
    System.out.println("Hello Guys");
  }
}

Lab162.java​

class Lab162 {

  public static void main(String[] args) {
    if (false) System.out.println("IF BLOCK");
    System.out.println("Hello Guys");
  }
}

Lab163.java​

class Lab163 {

  public static void main(String[] args) {
    if (false) {
      System.out.println("IF BLOCK");
      System.out.println("Hello Guys");
    }
  }
}

Lab164.java​

class Lab164 {

  public static void main(String[] args) {
    int a = 99;
    if (a == 99) System.out.println("Value is 99");
    System.out.println("Hello Guys");
  }
}

Lab165.java​

class Lab165 {

  public static void main(String[] args) {
    int a = 88;
    if (a == 99) System.out.println("Value is 99");
    System.out.println("Hello Guys");
  }
}

Lab166.java​

class Lab166 {

  public static void main(String[] args) {
    int a = 99;
    if (a == 99) {
      int b = 12;
      System.out.println(b);
      System.out.println(a);
    }
    System.out.println(a);
  }
}

Lab167.java​

class Lab167 {

  public static void main(String[] args) {
    int a = 99;
    if (a == 99) {
      int b = 12;
      System.out.println(b);
      System.out.println(a);
    }
    System.out.println(a);
    System.out.println(b); // Error: b is not accessible here
  }
}

Lab168.java​

class Lab168 {

  public static void main(String[] args) {
    int a = 42;
    if (a % 2 == 0) System.out.println("Value is EVEN");
    else System.out.println("Value is ODD");
  }
}

Key Learnings​

  • if(true) → always executes IF block
  • if(false) → never executes IF block
  • Without {}, only one statement belongs to if
  • Variables inside {} block → block scope only
  • Accessing block variable outside → compile-time error
  • if-else helps in decision making (e.g., even/odd check)

Lab169.java​

class Lab169 {
    public static void main(String[] args) {
        int a = 0;

        if (a++==0)
        System.out.println("Zero");
        elseif (a++==1)
        System.out.println("One");
        else
        System.out.println("Not Matching");

        System.out.println(a);
    }
}


Lab170.java​

class Lab170 {
    public static void main(String[] args) {
        int a = 1;

        if (++a==1)
        System.out.println("One");
        elseif (++a==2)
        System.out.println("Two");
        else
        System.out.println("Not Matching");

        System.out.println(a);
    }
}


Lab171.java​

class Lab171 {

  public static void main(String[] args) {
    if (0) System.out.println("IF BLOCK");
    System.out.println("Hello Guys");
  }
}

Lab172.java​

class Lab172 {

  public static void main(String[] args) {
    int a = 10;
    int b = 20;

    if (a > b) System.out.println(
      "Max value between " + a + " and " + b + " is " + a
    );
    else System.out.println(
      "Max value between " + a + " and " + b + " is " + b
    );
  }
}

Lab173.java​

class Lab173 {
    public static void main(String[] args) {
        int a = 10;
        int b = 20;
        int c = 15;
        int max = 0;

        if (a>b&&a>c)
        max=a;
        elseif (b>a&&b>c)
        max=b;
        else
        max=c;

        System.out.println("Max value is "+max);
    }
}


🔑 Key Learnings​

  • a++ → post-increment (value used first, then increment)
  • ++a → pre-increment (increment first, then use value)
  • if (0) → invalid (condition must be boolean in Java)
  • if-else-if ladder executes first matching condition only
  • Logical AND (&&) is used for multiple condition checks
  • Useful for finding max of numbers

2.9.1.2 switch Statement

  • Switch statement allows the program to select one action among multiple actions during program execution.

Syntax​

switch (variable/expression/value) {

    caseval1:
    // Statements
    break;

    caseval2:
    // Statements
    break;

    ...

    default:
    // Statements
}

Key Points​

  • First, the switch expression is evaluated.
  • Then it tries to find a matching case value.
  • If a matching case is found → corresponding statements are executed.
  • Otherwise → default block will be executed.

Allowed Data Types (up to Java 7)​

✔ Allowed:​

  • byte
  • short
  • char
  • int
  • enum (from Java 5)
  • String (from Java 7)

Not Allowed:​

  • long
  • float
  • double
  • boolean

Lab174.java​

class Lab174 {
    public static void main(String[] args) {
        int a = 3;

        switch (a) {

            case0:
            System.out.println("Sunday");
            break;

            case1:
            System.out.println("Monday");
            break;

            case2:
            System.out.println("Tuesday");
            break;

            case3:
            System.out.println("Wednesday");
            break;

            case4:
            System.out.println("Thursday");
            break;

            case5:
            System.out.println("Friday");
            break;

            case6:
            System.out.println("Saturday");
            break;

            default:
            System.out.println("Wrong Input");
        }
    }
}


Key Learnings​

  • break is used to stop fall-through behavior
  • Without break, execution continues to next cases
  • default works like else block
  • Best used when checking multiple fixed values

Lab175.java​

class Lab175 {

  public static void main(String[] args) {
    int a = 30;
    switch (a) {
    }

    char ch = 'A';
    switch (ch) {
    }

    byte by = 123;
    switch (by) {
    }

    short sh = 234;
    switch (sh) {
    }
  }
}

Lab176.java​

class Lab176 {

  public static void main(String[] args) {
    long a = 30;
    switch (a) {
    } // Invalid

    float f = 30.0F;
    switch (f) {
    } // Invalid

    double d = 30.0;
    switch (d) {
    } // Invalid

    boolean b = true;
    switch (b) {
    } // Invalid
  }
}

Lab177.java​

class Lab177 {
    public static void main(String[] args) {

        C oursec=Course.CORE;

        switch (c) {
            caseADV:
            System.out.println("100% PLACEMENT GUARANTEE");
            break;

            caseCORE:
            System.out.println("NO PLACEMENT GUARANTEE");
            break;
        }
    }
}

enumCourse {
    CORE,ADV
}


Lab178.java​

class Lab178 {

  public static void main(String[] args) {
    String loc = "MKR";

    switch (loc) {
      case "BTM":
        System.out.println("Branch Office");
        break;
      case "MKR":
        System.out.println("Head Office");
        break;
    }
  }
}

Lab179.java​

class Lab179 {
    public static void main(String[] args) {

        int a = 98;

        switch (a) {
            case98:
            System.out.println("Val - 98");
            break;

            case98:
            System.out.println("Val - 98");
            break;
        }
    }
}


Lab180.java​

class Lab180 {
    public static void main(String[] args) {

        int a = 98;
        int x = 96;

        switch (a) {

            case98:
            System.out.println("Val - 98");
            break;

            casex:
            System.out.println("Variable - x");
            break;
        }
    }
}


Key Learnings from this Page​

  • Allowed in switch: byte, short, char, int, enum, String
  • Not allowed: long, float, double, boolean
  • enum can be used in switch (Java 5+)
  • String can be used in switch (Java 7+)
  • Case labels must be:
    • constant values
    • unique (no duplicates)
  • Duplicate case → compile-time error
  • Variables (non-final) cannot be used in case

Lab181.java​

class Lab181 {
    public static void main(String[] args) {
        byte b = 20;

        switch (b) {
            case10:
            System.out.println("TEN");

            case20:
            System.out.println("TWENTY");
        }
    }
}


Lab182.java​

class Lab182 {
    public static void main(String[] args) {
        int a = 45;
        final int X = 20;

        switch (a) {

            case10:
            System.out.println("TEN");

            caseX:
            System.out.println("TWENTY");

            case'A':
            System.out.println("CHAR - A");

            case10+20+15:
            System.out.println("CONSTANT EXPR");

            default:
            System.out.println("DEFAULT");
        }
    }
}


Lab183.java​

class Lab183 {
    public static void main(String[] args) {
        int a = 10;
        final int X = 20;

        switch (a) {

            case10:
            System.out.println("TEN");
            break;

            caseX:
            System.out.println("TWENTY");
            break;

            case'A':
            System.out.println("CHAR - A");
            break;

            case10+20+15:
            System.out.println("CONSTANT EXPR");
            break;

            default:
            System.out.println("DEFAULT");
        }
    }
}


Lab184.java​

class Lab184 {
    public static void main(String[] args) {
        int a = 23;

        switch (a) {

            case10:
            System.out.println("TEN");
            break;

            default:
            System.out.println("DEFAULT");
            break;

            case10+10:
            System.out.println("TWENTY");
            break;
        }
    }
}


Key Learnings from this Page​

  • If break is not used, switch will fall through to next cases
  • final variables can be used in case labels
  • Case labels must be:
    • constant expressions
    • evaluated at compile time
  • Valid case labels:
    • literals (10)
    • characters ('A')
    • constant expressions (10 + 20 + 15)
    • final variables
  • default:
    • optional
    • can appear anywhere in switch

Lab185.java​

class Lab185 {

  public static void main(String[] args) {
    char ch = 'A';

    if (ch >= 65 && ch <= 90) {
      switch (ch) {
        case 'A':
        case 'E':
        case 'I':
        case 'O':
        case 'U':
          System.out.println("Character is Vowel");
          break;
        default:
          System.out.println("Character is Consonant");
      }
    } else {
      System.out.println("Invalid Alphabet");
    }
  }
}

Key Concept from This Program​

✔ Checking Character Type​

  • ch >= 65 && ch <= 90 → Ensures character is uppercase alphabet (A–Z) using ASCII values