Java Keywords List: Complete Guide to Reserved Words

In Java, keywords are special words that are reserved by the compiler. These keywords serve predefined purposes and cannot be used as identifiers, such as variable names, class names, or method names.

Using a keyword inappropriately will result in a compile-time error.

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🔍 What Are Java Keywords?

A keyword (also known as a reserved word) tells the Java compiler to treat it as part of the language syntax. You cannot redefine it, override it, or use it in custom identifiers.

Example:

int class = 10;  // ❌ Invalid: 'class' is a keyword

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📋 Complete List of Java Keywords

These 50 words are reserved by the Java language. They are case-sensitive and cannot be used for any other purpose.

abstract	assert	boolean	break
byte	case	catch	char
class	const*	continue	default
do	double	else	enum
extends	final	finally	float
for	goto*	if	implements
import	instanceof	int	interface
long	native	new	package
private	protected	public	return
short	static	strictfp	super
switch	synchronized	this	throw
throws	transient	try	void
volatile	while	—	—

* const and goto are reserved but not used in Java.

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🛠️ Usage Rules and Best Practices

✅ Do This

int count = 10;       // valid
String name = "Java"; // valid

❌ Avoid This

int for = 5;          // Error: 'for' is a keyword
String new = "Data";  // Error: 'new' is a keyword

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💡 Common Mistakes

Mistake	Fix
Using class, enum, or switch as identifiers	Rename to something else
Typing Class (uppercase) thinking it's different from class	Java is case-sensitive, but keywords are always lowercase
Using reserved keywords in libraries accidentally	Prefix with _ or use camelCase

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🎓 Interview Angle

• Q: Why can’t I use ‘new’ or ‘for’ as variable names in Java?
  A: Because they are reserved as part of the Java syntax. Using them would break parser logic and lead to ambiguity.

• Q: Are Java keywords case-sensitive?
  A: Yes. All keywords are lowercase. Public, Void, Main are not keywords.

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🧭 Java Version Relevance

Keyword	Introduced	Notes
Most keywords	Java 1.0	Included since the beginning
enum	Java 5	Introduced for enumerated types
assert	Java 1.4	Added for assertions
strictfp	Java 1.2	Ensures consistent floating-point precision
var	Java 10	Not a keyword but a reserved type name

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📝 Summary

• Java has 50 keywords, all reserved for internal use by the compiler.
• Using a keyword as an identifier will lead to errors.
• Two keywords (const and goto) are reserved but not currently in use.
• All keywords are lowercase and cannot be redefined.

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✅ Tip: When naming your variables or classes, always check against the list of Java keywords to avoid naming conflicts.