Java InteropTako Schotanus, Red Hat

Geecon: An Introduction to Ceylon

Combined sources

public class JavaClass {

int count(String name) { ... }

}

shared void run() {

value jc = JavaClass();

print( jc.count("thing") );

}

Geecon: An Introduction to Ceylon

Legacy code

• Maven

module “helloworld” 1.0 {

import org.hibernate.core “4.2.1.Final”;

import com.example.myjar “3.0”;

}

ceylon compile --rep aether helloworld/1.0

• Import-jarceylon import-jar --jar lib/myjar-3.0 com.example.myjar/3.0

Geecon: An Introduction to Ceylon

Primitive types

• Integer <-> long, int, short, byte

• Float <-> double, float

• Boolean <-> boolean

• Character --> int, char

• String <-> j.l.String

• No Byte type (might come in future?)

• Boxing with generics

Geecon: An Introduction to Ceylon

Special name handling

print(\iCONSTANT);

value v = \Isome_class()

import com.example {

constant = CONSTANT,

SomeClass = some_class }

print(constant);

value v = SomeClass()

Geecon: An Introduction to Ceylon

Null handling

public class JavaClass {

int foo(int param) { ... }

Integer bar(Integer param) { return null; }

}

Integer i1 = jc.foo(5);

Integer i2 = jc.foo(null); // Error

Integer? i3 = jc.bar(null);

Integer i4 = jc.bar(5); // Compiles Ok, runtime error

Geecon: An Introduction to Ceylon

Properties

public class JavaClass {

int getFoo() { ... }

int getBar() { ... }

void setBar(int bar) { ... }

void setBaz(int baz) { ... }

}

shared class ClassClass() {

Integer foo;

variable Integer bar;

void setBaz(Integer baz) { ... }

}

Geecon: An Introduction to Ceylon

Properties (contd.)

public class JavaClass {

int getFoo() { return 0; }

int getBar() { return b; }

void setBar(int bar) { ... }

void setBaz(int baz) { ... }

}

shared class ClassClass() {

Integer foo { return 0; }

Integer bar { return b; }

assign bar { ... }

void setBaz(Integer baz) { ... }

}

Geecon: An Introduction to Ceylon

Overloading

public class JavaClass {

void foo(int param) { ... }

void foo(String param) { ... }

}

jc.foo(5);

jc.foo(“bar”);

Ceylon doesn't have overloading but does support it for Java where possible

Geecon: An Introduction to Ceylon

Overloading (contd.)

public class JavaClass {

void foo(long param) { ... }

void foo(short param) { ... }

}

import java.lang { Short }

jc.foo(5);

jc.foo(Short(5).shortValue());

Geecon: An Introduction to Ceylon

JDK Modules (JigSaw)

• JDK divided in JigSaw compatible modules

• Always available but must be explicitly imported

module “helloworld” 1.0 {

import java.base “7”;

import javax.xml “7”;

}

import java.lang { Short }

import javax.xml { ... }

Geecon: An Introduction to Ceylon

Arrays

• BooleanArray --> boolean[ ]

• IntArray --> int[ ]

• ByteArray, CharArray, etc

• ShortArray(...).array --> Array<j.l.Short>

• Array<T>

Geecon: An Introduction to Ceylon

Annotations

import javax.annotation { postConstruct }

postConstruct shared void reset() {

// Clean up after ourselves

this.count = 0;

this.userNumber = 0;

}

• Integration with existing frameworks that use annotations possible

Geecon: An Introduction to Ceylon

ceylon.interop.java

• Part of the SDK

• Useful functions like– javaClassFromInstance()

– javaString()

– JavaIterable / JavaIterator– CeylonIterable / CeylonIterator

Geecon: An Introduction to Ceylon

JavaScript interop

• All revolves around dynamic

dynamic value target;

dynamic {

target = jQuery(“#target”);

target.select(function() { ... });

}

• Typed interfaces in the future?

Geecon: An Introduction to Ceylon