Basic Building Blocks of a Java Program

Introduction:

A Java program is made up of various components that define its logic, structure, and behavior. These are the essential building blocks you need to understand to write effective Java code.

                    Keywords
Identifiers
Data Types
Variables
Literals
Operators
Statements
Control Flow Statements
Comments
Indentation & Formatting
Class
Method
Objects
Packages

                

1. Keywords

Reserved words that have predefined meanings in Java. You cannot use them as identifiers.

Example: public, class, static, void, if, else

Click to learn all 50+ Java keywords

2. Identifiers

Names given to variables, classes, methods, etc. They help uniquely identify elements in a program.

Example: Student, main, totalMarks

Rules: Must not start with a digit, no special characters (except _, $)

Click to learn identifier rules & examples

3. Variables

Variables are named containers that store data in memory (RAM) during program execution. They allow programs to read, update, and manipulate values.

Example:

int a = 100;         // Declaration + Initialization  
a = 150;             // Assignment  
System.out.println(a);  // Using the variable

Click to learn more about variable rules and examples

4. Data Types

Define the kind of data a variable can store.

Primitive: int, float, char, boolean
Non-primitive: String, Array, Object

Click to explore Java data types in detail

5. Literals

Fixed values used in code — numbers, characters, strings, etc.

Example: 10, 'A', "Hello", true, 3.14

Click to learn types of literals

6. Operators

Symbols used to perform operations on data, such as arithmetic, logical, relational, etc.

Example: +, -, *, /, ==, &&

7. Statements

Instructions that Java executes, ending with a semicolon (;).

Examples:

System.out.println("Hello");
int x = 10;

Click to learn how Java executes statements

8. Control Flow Statements

These include decision-making and looping constructs used to control the execution flow of a program.

Conditional: if, else, else if, switch
Looping: for, while, do-while
Jumping: break, continue, return

Click to learn how control flow statements work

9. Comments

Non-executable lines used to describe what the code is doing. Helps in understanding code logic.

Types:

// Single-line
/* */ Multi-line
/** */ Documentation

Click to see how to use comments effectively

10. Indentation & Formatting

Improves code readability and clean structure. While ignored by the compiler, consistent indentation helps maintain code.

Tip: Use 2 or 4 spaces consistently per block.

Click to see formatting best practices

11. Class

The base unit of every Java program.
Defines structure and behavior via variables and methods.

public class MyClass {
    // code
}

12. Method

A block of code that performs a task.
The main method is the entry point.

public static void main(String[] args) {
    // execution starts here
}

13. Objects

An object is an instance of a class.
It has state (variables) and behavior (methods).

Student s = new Student();

14. Packages

Used to organize related classes together.
Helps avoid naming conflicts and improves structure.

package myproject;

Click to learn how Java packages help organize code

Understand with Example:

A Java program is made up of several small components like keywords, identifiers, operators, comments, literals, etc. Let’s look at a simple example to understand how all of them come together.

// This program calculates the total and average marks of a student
package studentApp;  // Package declaration
public class StudentMarks {  // 'class' is a keyword; 'StudentMarks' is an identifier
    public static void main(String[] args) {  // 'public', 'static', 'void' are keywords
        // Variable declarations with data types
        int math = 85;
        int science = 90;
        int english = 88;
        // Using operators to calculate total and average
        int total = math + science + english;
        double average = total / 3.0;
        // Output statements (Statements + Literals + Objects)
        System.out.println("Total Marks = " + total);
        System.out.println("Average Marks = " + average);
    }
}

What This Program Shows

Building Block	Shown in Example
Keywords	public, class, static, void, int, double, package
Identifiers	StudentMarks, math, science, total, main, studentApp
Variables	math, science, english, total, average
Data Types	int, double
Literals	85, 90, 88, 3.0, "Total Marks = "
Operators	+, /, =
Statements	Variable declarations, assignments, method calls ending with ;
Control Flow	None shown directly, but could include if-else, loops
Comments	// used throughout to explain code
Indentation & Format	Proper indentation for class, method, and logic
Class	public class StudentMarks { ... }
Method	public static void main(String[] args)
Objects	System.out is an object of PrintStream
Packages	package studentApp; at the top

Summary:

S.No.	Building Block	Description
1	Keywords	Reserved words with special meaning
2	Identifiers	Names for classes, variables, methods
3	Variables	Hold data during program execution
4	Data Types	Specify variable types
5	Literals	Fixed constant values
6	Operators	Perform operations on values/variables
7	Statements	Single executable instructions ending with ;
8	Control Flow Statements	if-else, switch, loops, break, continue, etc.
9	Comments	Explain code; ignored by compiler
10	Indentation & Formatting	Improves readability
11	Class	Blueprint of Java program
12	Method	Performs task; main method starts program
13	Objects	Instances of classes
14	Packages	Groups related classes into folders