Type inference

Since Java 10, it has become possible to infer types for the variables automatically by using var.

// stream will have the FileOutputStream type as inferred from its initializer
var stream = new FileOutputStream("file.txt");

// An equivalent declaration with an explicit type
FileOutputStream stream = new FileOutputStream("file.txt");

java.lang.Object

java.lang.Object is Java's top type. Superclass of all classes that do not declare a parent class. All values can be converted to this type, although for primitive values this involves autoboxing.

java.lang.String

java.lang.String is Java's basic string type. Immutable. Some methods treat each UTF-16 code unit as a "character", but methods to convert to an int[] that is effectively UTF-32 are also available.

java.lang.Throwable

java.lang.Throwable is supertype of everything that can be thrown or caught with Java's throw and catch statements.

Type import declaration

A type import declaration allows a named type to be referred to by a simple name rather than the full name that includes the package. Import declarations can be single type import declarations or import-on-demand declarations. Import declarations must be placed at the top of a code file after the package declaration.

package myPackage;

import java.util.Random; // Single type declaration

public class ImportsTest {
    public static void main(String[] args) {
        /* The following line is equivalent to
         * java.util.Random random = new java.util.Random();
         * It would've been incorrect without the import.
         */
        Random random = new Random();
    }
}

Import-on-demand declarations are mentioned in the code. A "type import" imports all the types of the package. A "static import" imports members of the package.

import java.util.*;  /*This form of importing classes makes all classes
    in package java.util available by name, could be used instead of the
    import declaration in the previous example. */
import java.*; /*This statement is legal, but does nothing, since there
    are no classes directly in package java. All of them are in packages
    within package java. This does not import all available classes.*/

Static import declaration

This type of declaration has been available since J2SE 5.0. Static import declarations allow access to static members defined in another class, interface, annotation, or enum; without specifying the class name:

import static java.lang.System.out; //'out' is a static field in java.lang.System

public class HelloWorld {
    public static void main(String[] args) {
        /* The following line is equivalent to
             System.out.println("Hi World!");
           and would have been incorrect without the import declaration. */
        out.println("Hello World!");
    }
}

Import-on-demand declarations allow to import all the fields of the type:

import static java.lang.System.*;
    /* This form of declaration makes all
       fields in the java.lang.System class available by name, and may be used instead
       of the import declaration in the previous example. */

Enum constants may also be used with static import. For example, this enum is in the package called screen:

public enum ColorName {
    RED, BLUE, GREEN
};

It is possible to use static import declarations in another class to retrieve the enum constants:

import screen.ColorName;
import static screen.ColorName.*;

public class Dots {
    /* The following line is equivalent to 'ColorName foo = ColorName.RED',
       and it would have been incorrect without the static import. */
    ColorName foo = RED;

    void shift() {
        /* The following line is equivalent to
           if (foo == ColorName.RED) foo = ColorName.BLUE; */
        if (foo == RED) foo = BLUE;
    }
}

if statement

if statements in Java are similar to those in C and use the same syntax:

if (i == 3) {
    doSomething();
}

if statement may include optional else block, in which case it becomes an if-then-else statement:

if (i == 3) {
    doSomething();
} else {
    doSomethingElse();
}

Like C, else-if construction does not involve any special keywords, it is formed as a sequence of separate if-then-else statements:

if (i == 3) {
    doSomething();
} else if (i == 2) {
    doSomethingElse();
} else {
    doSomethingDifferent();
}

Also, note that the ?: operator can be used in place of simple if statement, for example

int a = 1;
int b = 2;
int minVal = (a < b) ? a : b;

switch statement

Switch statements in Java can use byte, short, char, and int (note: not long) primitive data types or their corresponding wrapper types. Starting with J2SE 5.0, it is possible to use enum types. Starting with Java SE 7, it is possible to use Strings.^[2] Other reference types cannot be used in switch statements.

Possible values are listed using case labels. These labels in Java may contain only constants (including enum constants and string constants). Execution will start after the label corresponding to the expression inside the brackets. An optional default label may be present to declare that the code following it will be executed if none of the case labels correspond to the expression.

Code for each label ends with the break keyword. It is possible to omit it causing the execution to proceed to the next label, however, a warning will usually be reported during compilation.

switch (ch) {
    case 'A':
        doSomething(); // Triggered if ch == 'A'
        break;
    case 'B':
    case 'C':
        doSomethingElse(); // Triggered if ch == 'B' or ch == 'C'
        break;
    default:
        doSomethingDifferent(); // Triggered in any other case
        break;
}

var result = switch (ch) {
    case 'A' -> Result.GREAT;
    case 'B', 'C' -> Result.FINE;
    default -> throw new ThisIsNoGoodException();
};

var result = switch (ch) {
    case 'A':
        yield Result.GREAT;
    case 'B':
    case 'C':
        yield Result.FINE;
    default:
        throw new ThisIsNoGoodException();
};

while loop

In the while loop, the test is done before each iteration.

while (i < 10) {
    doSomething();
}

do ... while loop

In the do ... while loop, the test is done after each iteration. Consequently, the code is always executed at least once.

// doSomething() is called at least once
do {
    doSomething();
} while (i < 10);

for loop

for loops in Java include an initializer, a condition and a counter expression. It is possible to include several expressions of the same kind using comma as delimiter (except in the condition). However, unlike C, the comma is just a delimiter and not an operator.

for (int i = 0; i < 10; i++) {
    doSomething();
}
 
// A more complex loop using two variables
for (int i = 0, j = 9; i < 10; i++, j -= 3) {
    doSomething();
}

Like C, all three expressions are optional. The following loop is infinite:

for (;;) {
    doSomething();
}

Enhanced for loop

Enhanced for loops have been available since J2SE 5.0. This type of loop uses built-in iterators over arrays and collections to return each item in the given collection. Every element is returned and reachable in the context of the code block. When the block is executed, the next item is returned until there are no items remaining. Unlike C#, this kind of loop does not involve a special keyword, but instead uses a different notation style.

for (int i : intArray) {
    doSomething(i);
}

Labels

Labels are given points in code used by break and continue statements. Note that the Java goto keyword cannot be used to jump to specific points in the code.

start:
someMethod();

break statement

The break statement breaks out of the closest loop or switch statement. Execution continues in the statement after the terminated statement, if any.

for (int i = 0; i < 10; i++) {
    while (true) {
        break;
    }
    // Will break to this point
}

It is possible to break out of the outer loop using labels:

outer:
for (int i = 0; i < 10; i++) {
    while (true) {
        break outer;
    }
}
// Will break to this point

continue statement

The continue statement discontinues the current iteration of the current control statement and begins the next iteration. The following while loop in the code below reads characters by calling getChar(), skipping the statements in the body of the loop if the characters are spaces:

int ch;
while (ch == getChar()) {
    if (ch == ' ') {
        continue; // Skips the rest of the while-loop
    }

    // Rest of the while-loop, will not be reached if ch == ' '
    doSomething();
}

Labels can be specified in continue statements and break statements:

outer:
for (String str : stringsArr) {
    char[] strChars = str.toCharArray();
    for (char ch : strChars) {
        if (ch == ' ') {
            /* Continues the outer cycle and the next
            string is retrieved from stringsArr */
            continue outer;
        }
        doSomething(ch);
    }
}

return statement

The return statement is used to end method execution and to return a value. A value returned by the method is written after the return keyword. If the method returns anything but void, it must use the return statement to return some value.

void doSomething(boolean streamClosed) {
    // If streamClosed is true, execution is stopped
    if (streamClosed) {
        return;
    }
    readFromStream();
}

int calculateSum(int a, int b) {
    int result = a + b;
    return result;
}

return statement ends execution immediately, except for one case: if the statement is encountered within a try block and it is complemented by a finally, control is passed to the finally block.

void doSomething(boolean streamClosed) {
    try {
        if (streamClosed) {
            return;
        }
        readFromStream();
    } finally {
        /* Will be called last even if 
        readFromStream() was not called */
        freeResources();
    }
}

try-catch-finally statements

Exceptions are managed within try ... catch blocks.

try {
    // Statements that may throw exceptions
    methodThrowingExceptions();
} catch (Exception ex) {
    // Exception caught and handled here
    reportException(ex);
} finally {
    // Statements always executed after the try/catch blocks
    freeResources();
}

The statements within the try block are executed, and if any of them throws an exception, execution of the block is discontinued and the exception is handled by the catch block. There may be multiple catch blocks, in which case the first block with an exception variable whose type matches the type of the thrown exception is executed.

Java SE 7 also introduced multi-catch clauses besides uni-catch clauses. This type of catch clauses allows Java to handle different types of exceptions in a single block provided they are not subclasses of each other.

try {
    methodThrowingExceptions();
} catch (IOException | IllegalArgumentException ex) {
    //Both IOException and IllegalArgumentException will be caught and handled here
    reportException(ex);
}

If no catch block matches the type of the thrown exception, the execution of the outer block (or method) containing the try ... catch statement is discontinued, and the exception is passed up and outside the containing block (or method). The exception is propagated upwards through the call stack until a matching catch block is found within one of the currently active methods. If the exception propagates all the way up to the top-most main method without a matching catch block being found, a textual description of the exception is written to the standard output stream.

The statements within the finally block are always executed after the try and catch blocks, whether or not an exception was thrown and even if a return statement was reached. Such blocks are useful for providing clean-up code that is guaranteed to always be executed.

The catch and finally blocks are optional, but at least one or the other must be present following the try block.

try-with-resources statements

try-with-resources statements are a special type of try-catch-finally statements introduced as an implementation of the dispose pattern in Java SE 7. In a try-with-resources statement the try keyword is followed by initialization of one or more resources that are released automatically when the try block execution is finished. Resources must implement java.lang.AutoCloseable. try-with-resources statements are not required to have a catch or finally block unlike normal try-catch-finally statements.

try (FileOutputStream fos = new FileOutputStream("filename");
    XMLEncoder xEnc = new XMLEncoder(fos)) {
    xEnc.writeObject(object);
} catch (IOException ex) {
    Logger.getLogger(Serializer.class.getName()).log(Level.SEVERE, null, ex);
}

Since Java 9 it is possible to use already declared variables:

FileOutputStream fos = new FileOutputStream("filename");
XMLEncoder xEnc = new XMLEncoder(fos);
try (fos; xEnc) {
    xEnc.writeObject(object);
} catch (IOException ex) {
    Logger.getLogger(Serializer.class.getName()).log(Level.SEVERE, null, ex);
}

throw statement

The throw statement is used to throw an exception and end the execution of the block or method. The thrown exception instance is written after the throw statement.

void methodThrowingExceptions(Object obj) {
    if (obj == null) {
        // Throws exception of NullPointerException type
        throw new NullPointerException();
    }
    // Will not be called, if object is null
    doSomethingWithObject(obj);
}

Initializers

// Long syntax
int[] numbers = new int[] {20, 1, 42, 15, 34};
// Short syntax
int[] numbers2 = {20, 1, 42, 15, 34};

Multi-dimensional arrays

In Java, multi-dimensional arrays are represented as arrays of arrays. Technically, they are represented by arrays of references to other arrays.

int[][] numbers = new int[3][3];
numbers[1][2] = 2;

int[][] numbers2 = {{2, 3, 2}, {1, 2, 6}, {2, 4, 5}};

Due to the nature of the multi-dimensional arrays, sub-arrays can vary in length, so multi-dimensional arrays are not bound to be rectangular unlike C:

int[][] numbers = new int[2][]; //Initialization of the first dimension only

numbers[0] = new int[3];
numbers[1] = new int[2];

Declaration

class Foo {
    // Class members
}

class Foo { // Top-level class
    class Bar { // Inner class
    }
}

class Foo { // Top-level class
    static class Bar { // Nested class
    }
}

class Foo {
    void bar() {
        class Foobar {// Local class within a method
        }
    }
}

class Foo {
    void bar() {
        new Object() {// Creation of a new anonymous class extending Object
        };
    }
}

Instantiation

Non-static members of a class define the types of the instance variables and methods, which are related to the objects created from that class. To create these objects, the class must be instantiated by using the new operator and calling the class constructor.

Foo foo = new Foo();

Accessing members

Members of both instances and static classes are accessed with the . (dot) operator.

Accessing an instance member
Instance members can be accessed through the name of a variable.

String foo = "Hello";
String bar = foo.toUpperCase();

Accessing a static class member
Static members are accessed by using the name of the class or any other type. This does not require the creation of a class instance. Static members are declared using the static modifier.

public class Foo {
    public static void doSomething() {
    }
}

// Calling the static method
Foo.doSomething();

Modifiers

Modifiers are keywords used to modify declarations of types and type members. Most notably there is a sub-group containing the access modifiers.

• abstract - Specifies that a class only serves as a base class and cannot be instantiated.
• static - Used only for member classes, specifies that the member class does not belong to a specific instance of the containing class.
• final - Classes marked as final cannot be extended from and cannot have any subclasses.
• strictfp - Specifies that all floating-point operations must be carried out conforming to IEEE 754 and forbids using enhanced precision to store intermediate results.

Abstract class

This section is an excerpt from Abstract type § Java.[edit]

By default, all methods in all classes are concrete, unless the abstract keyword is used. An abstract class may include abstract methods, which have no implementation. By default, all methods in all interfaces are abstract, unless the default keyword is used. The default keyword can be used to specify a concrete method in an interface.

//By default, all methods in all classes are concrete, unless the abstract keyword is used.
public abstract class Demo {
    // An abstract class may include abstract methods, which have no implementation.
    public abstract int sum(int x, int y);

    // An abstract class may also include concrete methods.
    public int product(int x, int y) { 
        return x*y; 
    }
}

//By default, all methods in all interfaces are abstract, unless the default keyword is used.
interface DemoInterface {
    int getLength(); //The abstract keyword can be used here, though is completely useless
    
    //The default keyword can be used in this context to specify a concrete method in an interface
    default int product(int x, int y) {
        return x * y;
    }
}

public final class MyFinalClass {...}

public class ThisIsWrong extends MyFinalClass {...} // forbidden

Access modifiers

The access modifiers, or inheritance modifiers, set the accessibility of classes, methods, and other members. Members marked as public can be reached from anywhere. If a class or its member does not have any modifiers, default access is assumed.

public class Foo {
    int go() {
        return 0;
    }

    private class Bar {
    }
}

The following table shows whether code within a class has access to the class or method depending on the accessing class location and the modifier for the accessed class or class member:

Modifier	Same class or nested class	Other class inside the same package	Extended Class inside another package	Non-extended inside another package
private	yes	no	no	no
default (package private)	yes	yes	no	no
protected	yes	yes	yes	no
public	yes	yes	yes	yes

This image describes the class member scope within classes and packages.

Constructors and initializers

A constructor is a special method called when an object is initialized. Its purpose is to initialize the members of the object. The main differences between constructors and ordinary methods are that constructors are called only when an instance of the class is created and never return anything. Constructors are declared as common methods, but they are named after the class and no return type is specified:

class Foo {
    String str;

    Foo() { // Constructor with no arguments

        // Initialization
    }

    Foo(String str) { // Constructor with one argument
        this.str = str;
    }
}

Initializers are blocks of code that are executed when a class or an instance of a class is created. There are two kinds of initializers, static initializers and instance initializers.

Static initializers initialize static fields when the class is created. They are declared using the static keyword:

class Foo {
    static {
        // Initialization
    }
}

A class is created only once. Therefore, static initializers are not called more than once. On the contrary, instance initializers are automatically called before the call to a constructor every time an instance of the class is created. Unlike constructors instance initializers cannot take any arguments and generally they cannot throw any checked exceptions (except in several special cases). Instance initializers are declared in a block without any keywords:

class Foo {
    {
        // Initialization
    }
}

Since Java has a garbage collection mechanism, there are no destructors. However, every object has a finalize() method called prior to garbage collection, which can be overridden to implement finalization.

Methods

All the statements in Java must reside within methods. Methods are similar to functions except they belong to classes. A method has a return value, a name and usually some parameters initialized when it is called with some arguments. Similar to C++, methods returning nothing have return type declared as void. Unlike in C++, methods in Java are not allowed to have default argument values and methods are usually overloaded instead.

class Foo {
    int bar(int a, int b) {
        return (a*2) + b;
    }

    /* Overloaded method with the same name but different set of arguments */
    int bar(int a) {
        return a*2;
    }
}

A method is called using . notation on an object, or in the case of a static method, also on the name of a class.

Foo foo = new Foo();
int result = foo.bar(7, 2); // Non-static method is called on foo

int finalResult = Math.abs(result); // Static method call

The throws keyword indicates that a method throws an exception. All checked exceptions must be listed in a comma-separated list.

void openStream() throws IOException, myException { // Indicates that IOException may be thrown
}

public class Base
{
    public       void m1() {...}
    public final void m2() {...}

    public static       void m3() {...}
    public static final void m4() {...}
}

public class Derived extends Base
{
    public void m1() {...}  // OK, overriding Base#m1()
    public void m2() {...}  // forbidden

    public static void m3() {...}  // OK, hiding Base#m3()
    public static void m4() {...}  // forbidden
}

void printReport(String header, int... numbers) { //numbers represents varargs
    System.out.println(header);
    for (int num : numbers) {
        System.out.println(num);
    }
}

// Calling varargs method
printReport("Report data", 74, 83, 25, 96);

Fields

Fields, or class variables, can be declared inside the class body to store data.

class Foo {
    double bar;
}

Fields can be initialized directly when declared.

class Foo {
    double bar = 2.3;
}

Inheritance

Classes in Java can only inherit from one class. A class can be derived from any class that is not marked as final. Inheritance is declared using the extends keyword. A class can reference itself using the this keyword and its direct superclass using the super keyword.

class Foo {

}

class Foobar extends Foo {

}

If a class does not specify its superclass, it implicitly inherits from java.lang.Object class. Thus all classes in Java are subclasses of Object class.

If the superclass does not have a constructor without parameters the subclass must specify in its constructors what constructor of the superclass to use. For example:

class Foo {
    public Foo(int n) {
        // Do something with n
    }
}

class Foobar extends Foo {
    private int number;
    // Superclass does not have constructor without parameters
    // so we have to specify what constructor of our superclass to use and how

    public Foobar(int number) {
        super(number);
        this.number = number;
    }
}

class Operation {
    public int doSomething() {
        return 0;
    }
}

class NewOperation extends Operation {
    @Override
    public int doSomething() {
        return 1;
    }
}

package org.dwwwp.test;

/**
 * @author jcrypto
 */
public class AbstractClass {
    private static final String hello;

    static {
        System.out.println(AbstractClass.class.getName() + ": static block runtime");
        hello = "hello from " + AbstractClass.class.getName();
    }

    {
        System.out.println(AbstractClass.class.getName() + ": instance block runtime");
    }

    public AbstractClass() {
        System.out.println(AbstractClass.class.getName() + ": constructor runtime");
    }

    public static void hello() {
        System.out.println(hello);
    }
}

package org.dwwwp.test;

/**
 * @author jcrypto
 */
public class CustomClass extends AbstractClass {

    static {
        System.out.println(CustomClass.class.getName() + ": static block runtime");
    }

    {
        System.out.println(CustomClass.class.getName() + ": instance block runtime");
    }

    public CustomClass() {
        System.out.println(CustomClass.class.getName() + ": constructor runtime");
    }

    public static void main(String[] args) {
        CustomClass nc = new CustomClass();
        hello();
        //AbstractClass.hello();//also valid
    }
}

org.dwwwp.test.AbstractClass: static block runtime
org.dwwwp.test.CustomClass: static block runtime
org.dwwwp.test.AbstractClass: instance block runtime
org.dwwwp.test.AbstractClass: constructor runtime
org.dwwwp.test.CustomClass: instance block runtime
org.dwwwp.test.CustomClass: constructor runtime
hello from org.dwwwp.test.AbstractClass

Enumerations

This language feature was introduced in J2SE 5.0. Technically enumerations are a kind of class containing enum constants in its body. Each enum constant defines an instance of the enum type. Enumeration classes cannot be instantiated anywhere except in the enumeration class itself.

enum Season {
    WINTER, SPRING, SUMMER, AUTUMN
}

Enum constants are allowed to have constructors, which are called when the class is loaded:

public enum Season {
    WINTER("Cold"), SPRING("Warmer"), SUMMER("Hot"), AUTUMN("Cooler");

    Season(String description) {
        this.description = description;
    }

    private final String description;

    public String getDescription() {
        return description;
    }
}

Enumerations can have class bodies, in which case they are treated like anonymous classes extending the enum class:

public enum Season {
    WINTER {
        String getDescription() {return "cold";}
    },
    SPRING {
        String getDescription() {return "warmer";}
    },
    SUMMER {
        String getDescription() {return "hot";}
    },
    FALL {
        String getDescription() {return "cooler";}
    };
}

Implementing an interface

An interface is implemented by a class using the implements keyword. It is allowed to implement more than one interface, in which case they are written after implements keyword in a comma-separated list. Class implementing an interface must override all its methods, otherwise it must be declared as abstract.

interface RequestListener {
    int requestReceived();
}

class ActionHandler implements ActionListener, RequestListener {
    public void actionSelected(int action) {
    }

    public int requestReceived() {
    }
}

//Calling method defined by interface
RequestListener listener = new ActionHandler(); /*ActionHandler can be
                                   represented as RequestListener...*/
listener.requestReceived(); /*...and thus is known to implement
                            requestReceived() method*/

Functional interfaces and lambda expressions

These features were introduced with the release of Java SE 8. An interface automatically becomes a functional interface if it defines only one method. In this case an implementation can be represented as a lambda expression instead of implementing it in a new class, thus greatly simplifying writing code in the functional style. Functional interfaces can optionally be annotated with the @FunctionalInterface annotation, which will tell the compiler to check whether the interface actually conforms to a definition of a functional interface.

// A functional interface
@FunctionalInterface
interface Calculation {
    int calculate(int someNumber, int someOtherNumber);
}

// A method which accepts this interface as a parameter
int runCalculation(Calculation calculation) {
    return calculation.calculate(1, 2);
}

// Using a lambda to call the method
runCalculation((number, otherNumber) -> number + otherNumber);

// Equivalent code which uses an anonymous class instead
runCalculation(new Calculation() {
    @Override
    public int calculate(int someNumber, int someOtherNumber) {
        return someNumber + someOtherNumber;
    }
})

Lambda's parameters types don't have to be fully specified and can be inferred from the interface it implements. Lambda's body can be written without a body block and a return statement if it is only an expression. Also, for those interfaces which only have a single parameter in the method, round brackets can be omitted.^[8]

// Same call as above, but with fully specified types and a body block
runCalculation((int number, int otherNumber) -> {
    return number + otherNumber;
});

// A functional interface with a method which has only a single parameter
interface StringExtender {
    String extendString(String input);
}

// Initializing a variable of this type by using a lambda
StringExtender extender = input -> input + " Extended";

Method references

It is not necessary to use lambdas when there already is a named method compatible with the interface. This method can be passed instead of a lambda using a method reference. There are several types of method references:

The code above which calls runCalculation could be replaced with the following using the method references:

runCalculation(Integer::sum);

Inheritance

Interfaces can inherit from other interfaces just like classes. Unlike classes it is allowed to inherit from multiple interfaces. However, it is possible that several interfaces have a field with the same name, in which case it becomes a single ambiguous member, which cannot be accessed.

/* Class implementing this interface must implement methods of both
ActionListener and RequestListener */
interface EventListener extends ActionListener, RequestListener {    
}

Default methods

Java SE 8 introduced default methods to interfaces which allows developers to add new methods to existing interfaces without breaking compatibility with the classes already implementing the interface. Unlike regular interface methods, default methods have a body which will get called in the case if the implementing class doesn't override it.

interface StringManipulator {
    String extendString(String input);
    
    // A method which is optional to implement
    default String shortenString(String input) {
        return input.substring(1);
    }
}

// This is a valid class despite not implementing all the methods
class PartialStringManipulator implements StringManipulator {
    @Override
    public String extendString(String input) {
        return input + " Extended";
    }
}

Static methods

Static methods is another language feature introduced in Java SE 8. They behave in exactly the same way as in the classes.

interface StringUtils {
    static String shortenByOneSymbol(String input) {
        return input.substring(1);
    }
}

StringUtils.shortenByOneSymbol("Test");

Private methods

Private methods were added in the Java 9 release. An interface can have a method with a body marked as private, in which case it will not be visible to inheriting classes. It can be called from default methods for the purposes of code reuse.

interface Logger {
    default void logError() {
        log(Level.ERROR);
    }

    default void logInfo() {
        log(Level.INFO);
    }

    private void log(Level level) {
        SystemLogger.log(level.id);
    }
}

Annotations

Annotations in Java are a way to embed metadata into code. This language feature was introduced in J2SE 5.0.

@interface BlockingOperations {
}

@interface BlockingOperations {
    boolean fileSystemOperations();
    boolean networkOperations() default false;
}

@BlockingOperations(/*mandatory*/ fileSystemOperations,
/*optional*/ networkOperations = true)
void openOutputStream() { //Annotated method
}

@Unused // Shorthand for @Unused()
void travelToJupiter() {
}

/* Equivalent for @BlockingOperations(fileSystemOperations = true).
networkOperations has a default value and
does not have to be assigned a value */

@BlockingOperations(true)
void openOutputStream() {
}