Forem: silambarasan rajendran

day-40: Conditional Statements in Java

silambarasan rajendran — Thu, 08 May 2025 04:16:11 +0000

Conditional statements allow you to control the flow of your program based on different conditions. Java supports the following types:

1). if statement
2). if-else statement
3). if-else-if ladder
4). Nested if
5). switch-case statement

*1). if Statement *
Executes a block of code only if the condition is true.

Syntax

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

Example

int age = 18;
if (age >= 18) {
    System.out.println("You are an adult.");
}

Output:
You are an adult.

*2). if-else Statement *
Executes one block if the condition is true, and another if false.

Syntax

if (condition) {
    // Code if true
} else {
    // Code if false
}

Example

int num = 10;
if (num % 2 == 0) {
    System.out.println("Even");
} else {
    System.out.println("Odd");
}

Output:
Even

3). if-else-if Ladder
Checks multiple conditions in sequence.

Syntax

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

Example (Grading System)

int marks = 85;
if (marks >= 90) {
    System.out.println("Grade A");
} else if (marks >= 80) {
    System.out.println("Grade B");
} else if (marks >= 70) {
    System.out.println("Grade C");
} else {
    System.out.println("Grade D");
}

Output:
Grade B

4). Nested if
An if inside another if.

Syntax

if (condition1) {
    if (condition2) {
        // Code if both conditions are true
    }
}

Example (Login System)

String username = "admin";
String password = "12345";

if (username.equals("admin")) {
    if (password.equals("12345")) {
        System.out.println("Login successful!");
    } else {
        System.out.println("Wrong password.");
    }
} else {
    System.out.println("Invalid username.");
}

Output:
Login successful!

5). switch-case Statement
Used when you have multiple conditions based on a single variable.

Syntax

switch (variable) {
    case value1:
        // Code for value1
        break;
    case value2:
        // Code for value2
        break;
    default:
        // Code if no case matches
}

Example (Day of Week)

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Invalid day");
}

Output:
Wednesday

Important Notes on switch-case:
break prevents "fall-through" (execution of subsequent cases).

default runs if no case matches.

Java 14+ supports switch expressions (simplified syntax).

Key Takeaways
Statement Use Case
if Single condition check
if-else Two possible outcomes
if-else-if Multiple conditions
Nested if Conditions inside conditions
switch-case Multiple fixed-value checks
Common Mistakes to Avoid
❌ Using = instead of ==

if (x = 5) → Wrong (assignment)
if (x == 5) → Correct (comparison)

❌ Missing break in switch-case

Causes unintended fall-through.

❌ Comparing strings with ==
Use str1.equals(str2) instead.

When to Use What?
Use if-else for range-based conditions (e.g., age > 18).
Use switch-case for fixed-value checks (e.g., day == 3).

Ternary Operator vs. if Statement in Java
Both are used for conditional logic, but they serve different purposes.

1). Ternary Operator (? :)
A shorthand for simple if-else conditions.
Returns a value (used in assignments).

Syntax
variable = (condition) ? valueIfTrue : valueIfFalse;

Example

int age = 18;
String status = (age >= 18) ? "Adult" : "Minor";
System.out.println(status); // Output: "Adult"

When to Use?
✔ Short, simple conditions (e.g., setting a variable).
✔ Avoids multiple lines of if-else.

Limitations
❌ Cannot execute multiple statements.
❌ Less readable for complex conditions.

2). if Statement
Used for general conditional logic.
Can execute multiple statements.

Syntax

if (condition) {
    // code if true
} else {
    // code if false
}

Example

int age = 18;
if (age >= 18) {
    System.out.println("Adult");
    System.out.println("You can vote!");
} else {
    System.out.println("Minor");
}

When to Use?
✔ Complex conditions (multiple checks).
✔ When you need multiple statements inside a branch.

Key Differences
Feature Ternary Operator (? :) if Statement
Purpose Returns a value Executes code blocks
Best for Simple conditions Complex logic
Multi-line ❌ No ✔ Yes
Readability Good for short conditions Better for long logic
When to Choose Which?
Use Ternary → Assigning values based on a condition.

java
int discount = (isMember) ? 10 : 0;
Use if → Multiple operations or nested conditions.

if (temperature > 30) {
    System.out.println("Hot");
    turnOnAC();
} else {
    System.out.println("Cool");
}

Advanced: Nested Ternary (Avoid if Possible)

int num = 10;
String result = (num > 0) ? "Positive" : (num < 0) ? "Negative" : "Zero";
System.out.println(result); // "Positive"

⚠ Warning: Nested ternaries reduce readability. Prefer if-else for clarity.

Final Advice
Ternary → Best for one-liners (e.g., variable assignments).

if → Best for complex logic (multiple conditions/statements).

----------------------------------- assisted by ai ---------------------------------------

day-34: looping statements in java

silambarasan rajendran — Wed, 30 Apr 2025 05:54:53 +0000

== --> Compares Values (Variables)

Can we compare Objects?

What is the difference between variables and objects?

What is Variable?
Named Container to store Data

What is Object?
Real Time Entity / Physical Entity / Sample of a class / Instance of a class / Memory Reference of a class / Combination of States and Behaviours

Can we compare Objects?
Yes, we can Objects.

Passing Objects as arguments:

==
compare --> positive, negative, neutral

equals --> true / false

what is this keyword?
this keyword refers to current object.

How do you call non-static methods in a class?
By using objects.
object.method_name()

player1.equals(player2);
player1.equals(player2);

public boolean equals(Players player2){
return false;
}

Where cant we use this keyword?
Inside static blocks - static methods

Where can we use this keyword?
non-static methods

== --> equals() method

Primitive Datatypes --> ==
Non-primitive datatypes --> equals()

Non-Primitive Datatypes are nothing but classes.

We can pass the object as parameter:

package learning1;

public class Muthu {
    int capacity; 
    int price; 

    public static void main(String[] args) {
        Silambarasan bike = new Silambarasan();
        Muthu muthu = new Muthu(); 
        muthu.travel(bike);
        Muthu waterBottle = new Muthu(); 
        waterBottle.capacity = 500; 
        waterBottle.price = 50; 
        muthu.drink(waterBottle);

    }

    private void drink(Muthu waterBottle) {
        System.out.println("Price is " + waterBottle.price);    
    }

    private void travel(Silambarasan bike) {
        bike.ride();
        System.out.println(bike.name);
        bike.fill_petrol();
        //bike.sell();  
    }
}


package learning1;

public class Silambarasan {

    String name = "bajaj";

    private void sell(){
        System.out.println("Planning to sell ");
    }

    public void ride(){
        System.out.println("Long Ride to Pondy");
    }

    public void fill_petrol(){
        System.out.println("Tank Full");
    }

    public void service_bike(){
        System.out.println("Bike Service");
    }
}

Switch Case:

int day = 3;

        if (day == 1) {
            System.out.println("Monday");
        } else if (day == 2) {
            System.out.println("Tuesday");
        } else if (day == 3) {
            System.out.println("Wednesday");
        } else if (day == 4) {
            System.out.println("Thursday");
        } else if (day == 5) {
            System.out.println("Friday");
        } else if (day == 6) {
            System.out.println("Saturday");
        } else if (day == 7) {
            System.out.println("Sunday");
        } else {
            System.out.println("Invalid day number");
        }


public class Control_FlowState {

    public static void main(String[] args) {

        int day = 3;

        switch (day) {
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            default:
                System.out.println("Invalid day number");
                break;
        }
    }
}

Work around:
switch-case: Task:

1) day = 1, day = 2, day = 3
Wednesday
2) Remove break from case 1, from case 2, from case 3
If we remove the break statement, process execute the all the conditions.

Monday
Tuesday
Wednesday
Invalid day number

3) Move default just above any case block.
No, Changes
4) Remove break statement from default.
No, Changes
5) Instead of using int day, try using float values.
java.lang.Error: Unresolved compilation problem

----------------------------- End of the Blog ----------------------

Day-33: Conditional Statements in java

silambarasan rajendran — Wed, 30 Apr 2025 05:04:36 +0000

Beginner: Repeated Reading: Base Twist:

DON'T SAY I DON'T KNOW
ALWAYS SAY LET ME TRY
DON'T THINK ABOUT ENTIRE OUTPUT
THINK ABOUT VERY NEXT STEP
KNOWN TO UNKNOWN
WRITE DOWN THE KNOWN STEPS
THINK ABOUT VARIABLE, ADD IF IT IS NECESSARY
MICRO TO MACRO

1). Normal Statements
2). Conditional Statements
3). Control Flow Statements

Good Bad Ugly
Gangers

if GBU -->
else if Gangers -->

if statement should definitely have else if part - True
else if statement should definitely have else part - True

if it rains, take umbrella
else

else if part should definitely have if part - True

else part should definitely have else if part - False
else part should definitely have if part - True

else part should definitely have either if or else if or both - True

if(no1>no2)
else

if(no1>no2)
else if(no2>no1)
else

else part is mandatory / Compulsory always - False

How many else if block can one if block have?
How many else block can one if block have?

else block should be added ONLY at the end of all if blocks True / False

if(sslc_1>sslc_2) --> if sslc_1 is greater than sslc_2

1). Basic if Condition (Check Even/Odd):

public class EvenOddCheck {
    public static void main(String[] args) {
        int number = 10;

        if (number % 2 == 0) {
            System.out.println(number + " is even.");
        } else {
            System.out.println(number + " is odd.");
        }
    }
}

2). if-else if Ladder (Grade Calculator)

public class GradeCalculator {
    public static void main(String[] args) {
        int marks = 85;

        if (marks >= 90) {
            System.out.println("Grade: A");
        } else if (marks >= 80) {
            System.out.println("Grade: B");
        } else if (marks >= 70) {
            System.out.println("Grade: C");
        } else {
            System.out.println("Grade: D");
        }
    }
}

3). Nested if (Login System)

public class LoginSystem {
    public static void main(String[] args) {
        String username = "admin";
        String password = "12345";

        if (username.equals("admin")) {          // Outer if
            if (password.equals("12345")) {     // Nested if
                System.out.println("Login successful!");
            } else {
                System.out.println("Wrong password.");
            }
        } else {
            System.out.println("Invalid username.");
        }
    }
}

Note: Uses String.equals() for comparison (not ==).

Key Takeaways:
1). Basic if-else: Single condition check.
2). if-else if: Multiple conditions (evaluated top-down).
3). Nested if: Condition inside another condition.

Common Pitfalls to Avoid:
Using = (assignment) instead of == (comparison).
Forgetting braces {} for multi-line blocks.
Comparing strings with == (use .equals() instead).

Re-call the previous statements:
Objects will call Constructors by default.
Child Object behaves as Parent Object is known as Inheritance.

Child Object = Parent Object
If both the statements are correct, My Question is:

Should Child Object call Constructor in Parent Class? Yes / No

Consider I have many constructors in Parent Class. In that case, which constructor will be called by Child Object?

Usually which constructor will be called when we create Objects? [Consider we have multiple constructors]
Constructor which has matching Arguments will be called.

new SuperMarket(10, "Rice", 5);

-------------------------- End of Blog ------------------------------

day-32: Getter and Setter Methods in Java - Simple Example

silambarasan rajendran — Wed, 23 Apr 2025 03:01:09 +0000

Getters and Setters in Java
Getters and setters are methods used to access (get) and modify (set) private variables in a class. They are a key part of encapsulation, which hides the internal state of an object and allows controlled access through methods.

Why Use Getters & Setters?

✔ Control access to private variables
✔ Add validation before setting values
✔ Make code more maintainable

Example: Person Class with Getter & Setter

public class Jewellery_shop {

    private int gold_rate;

    // Getter method (must return gold_rate)
    public int getGoldRate() {
        return gold_rate;
    }

    // Setter method
    public void setGoldRate(int gold_rate) {
        this.gold_rate = gold_rate;
        System.out.println("Gold Rate set to: " + gold_rate);
    }
}


public class Customer {

    public static void main(String[] args) {
        Jewellery_shop js = new Jewellery_shop();

        System.out.println("Initial Gold Rate: " + js.getGoldRate());

        // Set new rate
        js.setGoldRate(90);

        // Print updated rate
        System.out.println("Updated Gold Rate: " + js.getGoldRate());
    }
}

Best Practices / Rules for Getters and Setters:
✅ Naming Convention:
Getter: getVariableName()
Setter: setVariableName(Type value)

✅ Return Type:
Getter: Should return the variable (not void)
Setter: Should be void and accept one parameter

✅ Encapsulation Rule:
Keep your variables private
Access them via public getters and setters

---------------- Doc Asssite by AI -------------------------------

day-31: Getter and Setter Methods in Java - Simple Example

silambarasan rajendran — Wed, 23 Apr 2025 02:59:02 +0000

Why Use Getters & Setters?

✔ Control access to private variables
✔ Add validation before setting values
✔ Make code more maintainable

Example: Person Class with Getter & Setter

public class Jewellery_shop {

    private int gold_rate;

    // Getter method (must return gold_rate)
    public int getGoldRate() {
        return gold_rate;
    }

    // Setter method
    public void setGoldRate(int gold_rate) {
        this.gold_rate = gold_rate;
        System.out.println("Gold Rate set to: " + gold_rate);
    }
}


public class Customer {

    public static void main(String[] args) {
        Jewellery_shop js = new Jewellery_shop();

        System.out.println("Initial Gold Rate: " + js.getGoldRate());

        // Set new rate
        js.setGoldRate(90);

        // Print updated rate
        System.out.println("Updated Gold Rate: " + js.getGoldRate());
    }
}

Best Practices / Rules for Getters and Setters:
✅ Naming Convention:
Getter: getVariableName()
Setter: setVariableName(Type value)

✅ Return Type:
Getter: Should return the variable (not void)
Setter: Should be void and accept one parameter

✅ Encapsulation Rule:
Keep your variables private
Access them via public getters and setters

---------------- Doc Asssite by AI -------------------------------

day-31: this, super and inner class in java

silambarasan rajendran — Tue, 22 Apr 2025 03:24:30 +0000

The "this" Keyword in Java
The this keyword in Java is a reference variable that refers to the current object of a class.
It has several important uses:

Main Uses of this:
1). To refer to current class instance variables (to resolve ambiguity between instance variables and parameters)

public class Student {
    String name;

    public Student(String name) {
        this.name = name; // 'this.name' refers to instance variable
    }
}

2). To invoke current class constructor (constructor chaining)

public class Rectangle {
    int width, height;

    public Rectangle() {
        this(10, 10); // calls parameterized constructor
    }

    public Rectangle(int width, int height) {
        this.width = width;
        this.height = height;
    }
}

Important Notes

a). this cannot be used in a static context (static methods or static blocks)

b). this is automatically added by the compiler in many cases (like when calling instance methods)

c). It helps make code more readable and resolves naming conflicts

d). In event handling or anonymous classes, this can refer to different objects, so you might need to qualify it with the class name (e.g., ClassName.this)

Understanding this is fundamental to proper object-oriented programming in Java.

The "super" Keyword in Java:
The super keyword in Java is a reference variable that refers to the immediate parent class object. It's used to access parent class members (fields, methods, and constructors) from a subclass.

Main Uses of super
1). Accessing Parent Class Variables
Used when child and parent classes have fields with the same name:

class Parent {
    String color = "white";
}

class Child extends Parent {
    String color = "black";

    void printColor() {
        System.out.println(super.color); // prints "white" (parent)
        System.out.println(color);       // prints "black" (child)
    }
}

2). Calling Parent Class Methods

Used to call overridden methods from the parent class:

class Parent {
    void display() {
        System.out.println("Parent method");
    }
}

class Child extends Parent {
    void display() {
        super.display(); // calls parent's display()
        System.out.println("Child method");
    }
}

Calling Parent Class Constructors

Used to invoke parent class constructor (must be the first statement in child constructor):

class Parent {
    Parent() {
        System.out.println("Parent constructor");
    }
}

class Child extends Parent {
    Child() {
        super(); // calls parent constructor (implicit if omitted)
        System.out.println("Child constructor");
    }
}

Important Notes About super

super() must be the first statement in a constructor if used

If you don't write super(), the compiler automatically inserts a call to the no-arg parent constructor

You can pass parameters to super() to call specific parent constructors:

super(parameter1, parameter2);

super cannot be used in static contexts (static methods or blocks)

Unlike this, super is not a reference to an object - it's a keyword for special compiler handling

super vs this
Feature super this
Reference Immediate parent class Current class instance
Constructor Calls parent constructor Calls current class constructor
Variables Accesses parent class variables Accesses current class variables
Methods Calls overridden parent methods Calls current class methods

Understanding super is essential for proper inheritance and method overriding in Java.

Inner Class in Java - Simple Explanation

An inner class is a class defined inside another class. It helps organize related classes together and can access all members (even private) of the outer class.

Why Use Inner Classes?

Better Encapsulation: Hide helper classes inside another class.

Access Outer Class Private Members: Inner classes can access private fields/methods of the outer class.

Cleaner Code: Group related classes logically.

Key Points
✔ Inner classes can be private, protected, or public.
✔ Non-static inner classes cannot have static members (except static final constants).
✔ Static nested classes can have static members.

Example in Real Life

Think of a Car (Outer Class) having an Engine (Inner Class). The Engine is part of the Car and can access its private components, but it doesn’t make sense to use the Engine outside the Car.

class Car {
    private String model = "Tesla";

    class Engine {
        void start() {
            System.out.println(model + "'s engine started!"); // Can access private model
        }
    }
}

Conclusion
Inner classes help in organizing code logically and provide better encapsulation. Use them when a class is only meaningful inside another class! 🚀

------------------------------ This is Doc assists by AI --------------------------------

day-30: enumeration in java

silambarasan rajendran — Mon, 21 Apr 2025 00:34:06 +0000

What is enumeration?
An enum type is a special data type that enables for a variable to be a set of predefined constants. The variable must be equal to one of the values that have been predefined for it.

In programming, an "enum type" (or enumeration) is a data type that consists of a set of named constants, allowing you to represent a fixed set of values, such as days of the week or colors.

What it is:
Fixed Set of Values: Enums define a specific, limited set of possible values for a variable.
Named Constants: Each value in the enum is represented by a named constant, making the code more readable and maintainable.
Type Safety: Enums provide type safety, ensuring that a variable can only hold one of the defined enum values, preventing errors.

Examples:
Days of the Week: enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }
Compass Directions: enum Direction { NORTH, SOUTH, EAST, WEST }
Color: enum Color { RED, GREEN, BLUE }
Status: enum Status { ACTIVE, INACTIVE, PENDING }

How it's used:

Readability:
Enums make code easier to understand by using meaningful names instead of raw numerical values.
Maintainability:
When the set of possible values changes, you only need to modify the enum definition, not multiple places in the code.
Error Prevention:
Enums help prevent errors by ensuring that a variable can only hold one of the predefined values.
Type Safety:
Enums enforce type safety, ensuring that variables of an enum type can only hold values of that enum type.

In Different Programming Languages:

Java: public enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }

day-28: Java Interface Explained: Rules, Real-World Examples, and Multiple Inheritance

silambarasan rajendran — Sun, 20 Apr 2025 12:39:40 +0000

What is interface in java?
Interface like contract between two of them.

Interface methods always in implement in different class.

You and company:
1). 2 days leave can taken
2). upskill

1). Interface is not class - True


public interface Company_rules {

   int leaves = 10;
   boolean variable_pay = true;

    public void work();
    public void rotate_shift();
    public void relocate();
    public void upskill();
    public void apply_leave();
        // method define and can't implement, no body

}

public interface Player_rules {

    public int player_rules();
    public int practice();
}

public class Amma {

    public void eat() {
        System.out.println("have you had your dinner...");  
    }
}


public class Employee extends Amma implements Company_rules, Player_rules {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Employee empl1 = new Employee();
         empl1.work();

         System.out.println(Company_rules.leave); 
// Static variable from the interface can be access via interface name with variable name

         System.out.println(Employee.variable_pay); 
// Static variable from the interface can be access via implement 
class name        

    }

    @Override // definition by someone and implements
    public void work() {
        // TODO Auto-generated method stub

    }

    @Override
    public void rotate_shift() {
        // TODO Auto-generated method stub

    }

    @Override 
    public void relocate() {
        // TODO Auto-generated method stub
           System.out.println("move to blr...");

    }

    @Override
    public void upskill() {
        // TODO Auto-generated method stub

    }

    @Override
    public void apply_leave() {
        // TODO Auto-generated method stub

    }
    @Override
    public int player_rules() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public int practice() {
        // TODO Auto-generated method stub
        return 0;
    }
}

// @override means - method can be create by some and implement by someone

2). If method is interface mode if we again abstract that will be consider as redundant method. - True

3). methods in interface
return datatypes - public void apply_leave();
arguments - public void apply_leave(int leave_days);
method signature - access modifier - public, private, default, protect, final and static.

Static is common for all. and it will be called by class name.

final methods cannot be overridden.
final fields cannot be changed.

So, Interface won't support Final Key word.
Private also won't support.

interface also supports local variables:
public void apply_leave(int number);

It will support global variables:
int leave = 10;
boolean variable_pay = true;

if variable name is italy format that is static, in interface all the variables are static.

Is java supports multiple inheritance? yes, not directly

public class Employee extends Amma implements Company_rules { 
// multiple inheritance

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Employee empl1 = new Employee();
         empl1.work();
         empl1.play();

    }
}

Static variable from the interface can be access via interface name with variable name

Static variable from the interface can be access via implement class name

    {
         System.out.println(Company_rules.leave); 
         System.out.println(Employee.variable_pay); 

   }

Class can be more than one interfaces

To create New Object:
Classname refer_name = new classname();
Calculator cal = new Calculator();

For validation purpose interface can verify the employee class.
This is also called as dynamic Biding.

interface_name from_interface_reference = new Class_name();
parent_class partent_Object = new parent_class();

     Company_rules manager = new Employee();
     manager.apply_leave(); //dynamic biding

     Amma object_amma = new Employee(); 
     object_amma.eat();

you are allocating the new place for your manager and coach to validate the their given method in your class.

Dynamic Binding example chart with teacher role:

---------------------------------- end of the blog ---------------------------------------

day-29: Java Interface Explained: Rules, Real-World Examples, and Multiple Inheritance

silambarasan rajendran — Sun, 20 Apr 2025 12:22:09 +0000

What is interface in java?
Interface like contract between two of them.

Interface methods always in implement in different class.

You and company:
1). 2 days leave can taken
2). upskill

1). Interface is not class - True


public interface Company_rules {

   int leaves = 10;
   boolean variable_pay = true;

    public void work();
    public void rotate_shift();
    public void relocate();
    public void upskill();
    public void apply_leave();
        // method define and can't implement, no body

}

public interface Player_rules {

    public int player_rules();
    public int practice();
}

public class Amma {

    public void eat() {
        System.out.println("have you had your dinner...");  
    }
}


public class Employee extends Amma implements Company_rules, Player_rules {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Employee empl1 = new Employee();
         empl1.work();

         System.out.println(Company_rules.leave); 
// Static variable from the interface can be access via interface name with variable name

         System.out.println(Employee.variable_pay); 
// Static variable from the interface can be access via implement 
class name        

    }

    @Override // definition by someone and implements
    public void work() {
        // TODO Auto-generated method stub

    }

    @Override
    public void rotate_shift() {
        // TODO Auto-generated method stub

    }

    @Override 
    public void relocate() {
        // TODO Auto-generated method stub
           System.out.println("move to blr...");

    }

    @Override
    public void upskill() {
        // TODO Auto-generated method stub

    }

    @Override
    public void apply_leave() {
        // TODO Auto-generated method stub

    }
    @Override
    public int player_rules() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public int practice() {
        // TODO Auto-generated method stub
        return 0;
    }
}