"Java" (External Evaluation System)

Details

Java Version 9.0 and higher is supported.
Java is a popular general-purpose programming language.
Java does not require configuration to use with ExternalEvaluate.

ExternalEvaluate Usage

ExternalEvaluate["Java",code] executes the code string in a Java REPL and returns the results as a Wolfram Language expression.

Data Types

The following Java built-in types are supported, exactly as they are in J/Link:

byte, char, short, long	Integer	integer
float, double	Real	real-valued number
boolean	True\|False	Boolean values
String	String	sequence of character values
Array	List	array of vaules
BigDecimal	Real	arbitrary-precision real number
BigInteger	Integer	arbitrary-sized integer
null	Null	null value
object	JavaObject	arbitrary Java objects
Expr	expression	arbitrary Wolfram Language expressions

Usage Notes

The Java runtime used by ExternalEvaluate is the same one used for J/Link operations like LoadJavaClass and JavaNew, allowing seamless interoperability between J/Link and ExternalEvaluate.
Classes made visible to J/Link via its AddToClassPath function are visible to Java code in ExternalEvaluate.
Java classes you define in ExternalEvaluate are automatically loaded into J/Link and can be used like any other Java classes.

Examples

open allclose all

Basic Examples (5)

Evaluate 2+2 in Java and return the result:

Call a Java method:

Arrays are returned as lists:

Objects that have no natural representation are returned as JavaObject expressions, just as in J/Link:

Type > and select Java from the drop-down menu to get a code cell that uses ExternalEvaluate to evaluate:

java.util.Arrays.stream(new int[]{1,2,3}).map(num -> num*num).toArray()

Scope (2)

You can define a Java method without wrapping it in a full class definition. Note that such method definitions are always public and static so you can drop the "public static" prefix:

String removeVowels(String s) { return s.replaceAll("[aeiou]", ""); }

Method definitions return an ExternalFunction object that you can call:

Define an entire class:

public class Node { private String data; private Node next; public Node(String data) { this.data = data; next = null; } public String getData() { return data; } public void setData(String data) { this.data = data; } public Node getNext() { return next; } public void setNext(Node next) { this.next = next; } }

Class definitions return J/Link JavaClass expressions that you can use directly in J/Link:

You can also call your new class directly from ExternalEvaluate:

new Node("foo")

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