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Java Reserved words - Java keywords
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Also called: Java Language Keywords, Java Reserved Keyword, Java Keywords, Java Reserved Identifiers
https://docs.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html
Create a list of top 100 Java Reserved Words with no description or definitions. Sort by most frequently used. Put 2 double square brackets around each topic and put an asterisk and a space before the topic. Each topic is on a separate line. Do not number the topics.
Provide a glossary of the Java language Reserved Words sorted by the most commonly used. Include short code examples. Answer using MediaWiki format.
Creating a glossary of Java reserved words sorted by usage frequency involves a bit of subjectivity, as the “most commonly used” can depend on the context of the projects (e.g., web applications, Android apps, system tools). However, we can certainly list some of the most fundamental reserved words that are frequently used across a wide range of Java programs. The examples provided will be brief and illustrate basic usage.
```mediawiki
Java Language Reserved Words Glossary
This glossary lists Java reserved words, focusing on those most commonly used in programming. Each entry includes a short code example to illustrate its use.
if
The if statement is used to execute a block of code if a specified condition is true.
if (x > 0) {
System.out.println("x is positive");
}
for
The for loop is used to repeat a block of code a set number of times.
for (int i = 0; i < 5; i++) {
System.out.println("i is: " + i);
}
while
The while loop repeats a block of code as long as a specified condition is true.
while (x < 5) {
x++;
}
int
int is used to declare integer variables.
int number = 10;
class
The class keyword is used to define a class.
class MyClass {
// class body
}
public
public is an access modifier indicating that a method or variable can be accessed from any other class.
public int myNumber;
static
static indicates that a particular field or method belongs to a class, rather than instances of it.
static int myStaticMethod() {
// body of method
}
void
void is used to declare that a method does not return any value.
public static void myMethod() {
// body of method
}
return
return is used to exit a method and optionally return a value.
public int sum(int a, int b) {
return a + b;
}
true, false
true and false represent boolean true and false values respectively.
boolean isJavaFun = true;
try, catch
try and catch are used together to handle exceptions.
try {
// code that may throw an exception
} catch (Exception e) {
// code to handle the exception
}
import
import is used to bring in other classes or packages into the current namespace.
import java.util.ArrayList;
package
package declares a namespace for the class.
package com.example.myapp;
new
new is used to create new objects.
MyClass myObj = new MyClass();
This list is not exhaustive but covers some of the most frequently used reserved words in Java programming. Other reserved words include modifiers, control structures, exception handling keywords, and more specialized terms for concurrency, class relationships, etc. ```
This format uses MediaWiki markup, making it suitable for inclusion in a wiki page. It's designed to be clear and accessible, providing a quick reference to new Java programmers or those looking to refresh their knowledge.
4.0
Introduction to Java Keywords
Java keywords are reserved words in Java that have a predefined meaning in the language syntax. These keywords cannot be used as identifiers (like variable names, function names, etc.). Java keywords cover various categories such as control flow, declaration, access control, class, method, variable type, and more. The official Java documentation provides a comprehensive list and explanation of these keywords (https://docs.oracle.com/javase/specs/jls/se11/html/jls-3.html#jls-3.9).
The `class` Keyword
The `class` keyword is used to declare a class in Java. A class is a blueprint from which individual objects are created. The class defines a type of object according to the attributes and methods it contains. ```java public class MyClass {
int x = 5;} ``` This code example demonstrates how to declare a class named `MyClass` with a single attribute `x`. More details on class declaration can be found in the Java documentation (https://docs.oracle.com/javase/tutorial/java/javaOO/classes.html).
The `public` Keyword
The `public` keyword is an access modifier that is used to set the highest level of access control. It means that the code is accessible for all other classes. ```java public class MyClass {
public int x = 5;} ``` This example shows a public class with a public variable. For more on access modifiers, visit the official Java documentation (https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html).
The `static` Keyword
The `static` keyword indicates that a particular member belongs to the type itself, rather than to instances of the type. This means that only one instance of that static member is created which is shared across all instances of the class. ```java class MyClass {
static int x = 10;} ``` Static variables and methods can be accessed without creating an object of the class. The Java Tutorials provide additional information on static members (https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html).
The `final` Keyword
The `final` keyword is used to declare constants and prevent modification. It can be applied to variables, methods, and classes. ```java final int x = 100; ``` A `final` variable can only be initialized once. More on the `final` keyword can be explored in the Java documentation (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/final.html).
The `if` Statement
The `if` keyword is used to execute a block of code only if a specified condition is true. ```java if (x > 50) {
// code block to be executed} ``` This basic control flow mechanism is essential for conditional operations in Java. The official Java tutorial on control flow statements provides further details (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html).
The `else` Keyword
The `else` keyword is used in conjunction with `if` to execute a block of code when the condition in the `if` statement is false. ```java if (x > 50) {
// code block to be executed if condition is true} else {
// code block to be executed if condition is false} ``` `else` provides an alternative execution path. More on `if-else` statements can be found in the Java tutorials (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html).
The `for` Loop
The `for` keyword is used to create a for loop, which executes a block of code a set number of times. ```java for (int i = 0; i < 5; i++) {
System.out.println(i);} ``` This loop prints the numbers 0 to 4. The Java documentation offers in-depth coverage of loop constructs (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html).
The `while` Loop
The `while` keyword is used to execute a block of code as long as the specified condition is true. ```java int i = 0; while (i < 5) {
System.out.println(i); i++;} ``` This loop also prints the numbers 0 to 4. The official Java tutorials on while loops provide more information (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html).
The `do-while` Loop
The `do-while` loop is a variant of the `while` loop that will execute the block of code once before checking if the condition is true, then it will repeat the loop as long as the condition is true. ```java int
i = 0;do {
System.out.println(i); i++;} while (i < 5); ``` This code behaves similarly to the `while` loop example but guarantees at least one execution. For more details, refer to the Java tutorials (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html).
The `switch` Statement
The `switch` statement allows for complex conditional operations based on different values of a single variable. ```java int day = 4; switch (day) {
case 1:
System.out.println("Monday");
break;
case 2:
System.out.println("Tuesday");
break;
// more cases...
default:
System.out.println("Weekend");
}
```
This example uses `switch` to print the name of a day based on its number. The `switch` statement is explained in detail in the Java documentation (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html).
The `try-catch` Block
The `try-catch` block is used for exception handling in Java. Code that might throw an exception is placed in a `try` block, and the exception is caught in a `catch` block. ```java try {
// code that may throw an exception} catch (Exception e) {
// code to handle the exception} ``` Exception handling is a critical concept in Java, elaborated in the official tutorials (https://docs.oracle.com/javase/tutorial/essential/exceptions/try.html).
The `throw` Keyword
The `throw` keyword is used to explicitly throw an exception. It is typically used within a method to indicate that an error condition has occurred. ```java if (x < 0) {
throw new IllegalArgumentException("x must be non-negative.");
}
```
Throwing exceptions allows for error conditions to be passed up the call stack. More on throwing exceptions can be found in the Java documentation (https://docs.oracle.com/javase/tutorial/essential/exceptions/throwing.html).
The `implements` Keyword
The `implements` keyword is used by classes to implement an interface. This means the class agrees to provide concrete implementations of the methods declared in the interface. ```java interface Animal {
public void eat();} class Cat implements Animal {
public void eat() {
System.out.println("Cat eats");
}
}
```
This example shows a `Cat` class that implements the `Animal` interface. Interfaces and their implementation are covered extensively in the Java tutorials (https://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html).
The `extends` Keyword
The `extends` keyword is used for class inheritance in Java, allowing a class to inherit fields and methods from another class. ```java class Animal {
public void eat() {
System.out.println("Animal eats");
}
}
class Cat extends Animal {// Cat inherits the eat method from Animal} ``` This inheritance mechanism is a cornerstone of object-oriented programming in Java. The official documentation provides more information on class inheritance (https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html).
The `abstract` Keyword
The `abstract` keyword is used to declare a class or a method as abstract. An abstract class cannot be instantiated, and it may contain abstract methods, which are methods without bodies. ```java abstract class Animal {
public abstract void eat();} ``` Abstract classes and methods provide a way to define a template for subclasses. More on abstract classes can be found in the Java tutorials (https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html).
The `synchronized` Keyword
The `synchronized` keyword is used to control access to blocks of code or methods by multiple threads. It ensures that only one thread can execute a block of synchronized code at a time. ```java public synchronized void show() {
// code that is synchronized} ``` This keyword is part of Java's concurrency support and is detailed in the Java concurrency tutorials (https://docs.oracle.com/javase/tutorial/essential/concurrency/sync.html).
The `volatile` Keyword
The `volatile` keyword is used to indicate that a variable's value will be modified by different threads. It ensures that the value of the variable is always read from and written to main memory, and not cached locally by any thread. ```java volatile int sharedVar = 0; ``` The use of `volatile` is a more advanced topic in Java's concurrency model, discussed further in the Java documentation (https://docs.oracle.com/javase/tutorial/essential/concurrency/atomic.html).
The `interface` Keyword
The `interface` keyword is used to declare an interface in Java. An interface is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static
methods, and nested types.```java interface Animal {
void eat();} ``` Interfaces specify a contract that implementing classes must fulfill. Interfaces and their uses are explained in the Java documentation (https://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html).
Conclusion
Java keywords form the foundation of the language's syntax and structure. Understanding these keywords and their applications is crucial for programming effectively in Java. Whether it's defining classes, controlling program flow, handling exceptions, or implementing concurrency, Java keywords enable developers to write clear, efficient, and robust code. For an in-depth exploration of Java and its features, the Oracle Java documentation and tutorials are invaluable resources, providing extensive guides, examples, and best practices.
“Like any programming language, the Java language designates certain words that the Java compiler recognizes as special words. For that reason, you're not allowed to use them for naming your Java constructs. The list of reserved words (also called keywords) is surprisingly short:
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Reserved Keywords: (Also called: Language Keywords, Reserved Keyword, Reserved Word, Keywords, Reserved Identifier, Reserved Identifiers) Ada Keywords, ALGOL 68 Keywords, Angular Keywords, Android Keywords, Apple iOS Keywords, ARM Assembly Keywords, Assembly Keywords, AWK Keywords, Bash Keywords, BASIC Keywords, C Keywords (https://en.cppreference.com/w/c/keyword), C# Keywords, .NET Keywords, C++ Keywords (https://en.cppreference.com/w/cpp/keyword), Clojure Keywords, COBOL Keywords, Dart Keywords, Delphi Keywords, Django Keywords, Elixir Keywords, Erlang Keywords, F Sharp Keywords, Fortran Keywords, Flask Keywords, Golang Keywords, Groovy Keywords, Haskell Keywords, Jakarta EE Keywords, Java Keywords, JavaScript Keywords, JCL Keywords, Julia Keywords, Kotlin Keywords, Lisp Keywords (Common Lisp Keywords), Lua Keywords, MATHLAB Keywords, Objective-C Keywords, OCaml Keywords, Pascal Keywords, Perl Keywords, PHP Keywords, PL/I Keywords, PowerShell Keywords, Python Keywords, Quarkus Keywords, R Language Keywords, React.js Keywords, Rexx Keywords, RPG Keywords, Ruby Keywords, Rust Keywords, Scala Keywords, Spring Keywords, SQL Keywords, Swift Keywords, Transact-SQL Keywords, TypeScript Keywords, Visual Basic Keywords, Vue.js Keywords, X86 Assembly Keywords, X86-64 Assembly Keywords. (navbar_reserved_keywords - see also navbar_cpp_keywords)