Each of these 50 keywords has a specific meaning in the Java programming language. You can't use a keyword for anything other than the meaning described in this table.

Also, you can't make up new meanings for the words false, null, and true. But for technical reasons, the words false, null, and true aren't called keywords. Whatever!

Keyword What It Does
abstract Indicates that the details of a class, a method, or an interface are given elsewhere in the code.
assert Tests the truth of a condition that the programmer believes is true.
boolean Indicates that a value is either true or false.
break Jumps out of a loop or switch.
byte Indicates that a value is an 8-bit whole number.
case Introduces one of several possible paths of execution in a switch statement.
catch Introduces statements that are executed when something interrupts the flow of execution in a try clause.
char Indicates that a value is a character (a single letter, digit, punctuation symbol, and so on) stored in 16 bits of memory.
class Introduces a class – a blueprint for an object.
const You can’t use this word in a Java program. The word has no meaning. Because it’s a keyword, you can’t create a const variable.
continue Forces the abrupt end of the current loop iteration and begins another iteration.
default Introduces a path of execution to take when no case is a match in a switch statement.
do Causes the computer to repeat some statements over and over again (for example, as long as the computer keeps getting unacceptable results).
double Indicates that a value is a 64-bit number with one or more digits after the decimal point.
else Introduces statements that are executed when the condition in an if statement isn’t true.
enum Creates a newly defined type a group of values that a variable can have.
extends Creates a subclass — a class that reuses functionality from a previously defined class.
final Indicates that a variable’s value cannot be changed, that a class’s functionality cannot be extended, or that a method cannot be overridden.
finally Introduces the last will and testament of the statements in a try clause.
float Indicates that a value is a 32-bit number with one or more digits after the decimal point.
for Gets the computer to repeat some statements over and over again (for example, a certain number of times).
goto You can’t use this word in a Java program. The word has no meaning. Because it’s a keyword, you can’t create a goto variable.
if Tests to see whether a condition is true. If it’s true, the computer executes certain statements; otherwise, the computer executes other statements.
implements Reuses the functionality from a previously defined interface.
import Enables the programmer to abbreviate the names of classes defined in a package.
instanceof Tests to see whether a certain object comes from a certain class.
int Indicates that a value is a 32-bit whole number.
interface Introduces an interface, which is like a class, but less specific. (Interfaces are used in place of the confusing multiple-inheritance feature that’s in C++.)
long Indicates that a value is a 64-bit whole number.
native Enables the programmer to use code that was written in another language (one of those awful languages other than Java).
new Creates an object from an existing class.
package Puts the code into a package — a collection of logically related definitions.
private Indicates that a variable or method can be used only within a certain class.
protected Indicates that a variable or method can be used in subclasses from another package.
public Indicates that a variable, class, or method can be used by any other Java code.
return Ends execution of a method and possibly returns a value to the calling code.
short Indicates that a value is a 16-bit whole number.
static Indicates that a variable or method belongs to a class, rather than to any object created from the class.
strictfp Limits the computer’s ability to represent extra large or extra small numbers when the computer does intermediate calculations on float and double values.
super Refers to the superclass of the code in which the word super appears.
switch Tells the computer to follow one of many possible paths of execution (one of many possible cases), depending on the value of an expression.
synchronized Keeps two threads from interfering with one another.
this A self-reference — refers to the object in which the word this appears.
throw Creates a new exception object and indicates that an exceptional situation (usually something unwanted) has occurred.
throws Indicates that a method or constructor may pass the buck when an exception is thrown.
transient Indicates that, if and when an object is serialized, a variable’s value doesn’t need to be stored.
try Introduces statements that are watched (during runtime) for things that can go wrong.
void Indicates that a method doesn’t return a value.
volatile Imposes strict rules on the use of a variable by more than one thread at a time.
while Repeats some statements over and over again (as long as a condition is still true).
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