Chapter 7: Java Basics ☕¶

This cheat sheet covers Java syntax and core features for Chapter 7 of the GSEB Std 12 Computer Studies syllabus.

🎯 Key Concepts¶

Java: High-level, object-oriented language developed by James Gosling (Sun Microsystems).
Bytecode: The platform-independent format (saved as .class) that runs on the JVM.
WORA: "Write Once, Run Anywhere."

Tool	Full Name	Description
`javac`	Java Compiler	Converts source code (`.java`) to bytecode (`.class`).
`java`	Java Interpreter	Executes the bytecode on the JVM.
`jdb`	Java Debugger	Helps find and fix errors in the code.
`javadoc`	Doc Generator	Automatically generates documentation from comments.
`appletviewer`	Applet Viewer	Used to view and test Java applets (older tech).

Keywords: Reserved words like class, public, int, static (50+ words).
Identifiers: Names for variables, classes, and methods. Must not start with a digit.
Literals: Constant values (e.g., 100, "hello", true).
Operators: Symbols like +, -, *, /.
Separators: Characters like ( ), { }, [ ], ;, ,.

Entry Controlled Loops: Condition checked before execution (for, while).
Exit Controlled Loops: Condition checked after execution (do-while).
break: Exits the loop immediately.
continue: Skips the rest of the current iteration and goes to the next.

MCQ Alert: Java uses Unicode (16-bit) characters, unlike C/C++ which use ASCII.
MCQ Alert: The javac command compiles; java command runs.
MCQ Alert: main() is the entry point and must return void.
MCQ Alert: Single quotes are for char ('A'), double quotes for String ("ABC").
MCQ Alert: Java is case-sensitive.

Board Exam Secret

GSEB frequently asks about "Exit Controlled" loops. Remember: do-while will execute at least once even if the condition is false!