Java Interop

Java interop

Scripts use Java classes directly. Under an access policy only the classes and methods it allows are visible.

Naming classes

import java.util.HashMap;       // one class per import, no * and no static imports

HashMap scores = new HashMap(); // a Java class works as a type
StringBuilder sb = new StringBuilder();   // java.lang needs no import
dyn date = new java.util.Date(0L);        // a full name works without import

A nested class is written through its outer class: java.util.Map.Entry, not imported.

Objects, methods, fields

import java.util.HashMap;

HashMap scores = new HashMap();
scores.put("ann", 10);
println(scores.get("ann"), scores.size());   // 10 1

StringBuilder sb = new StringBuilder();
sb.append("a").append(1).append(true);
println(sb.toString());                       // a1true

println(Math.sqrt(16), Integer.MAX_VALUE);    // 4.0 2147483647

• Overloads are picked by the argument values at the call: append(1) calls append(int), append(true) calls append(boolean).
• Numbers convert to the parameter's type (int, long, double, float...). A one-letter string passes as a char.
• Static methods and fields are used through the class: Math.max(1, 2), Integer.MAX_VALUE.

Properties

obj.name reads a public field, or calls getName() or isName(). Assigning obj.name = v sets a public field or calls setName(v).

dyn date = new java.util.Date(0L);
println(date.time);        // 0 - date.getTime()
dyn list = new java.util.ArrayList();
println(list.empty);       // true - list.isEmpty()

On a Java Map, m.key is a property too, not m.get("key"). Use m["key"] to read and write entries.

Functions, tables and arrays as Java values

Jumper value	Passed to a Java parameter of type
a function or lambda	any functional interface: Runnable, Comparator, Consumer, an interface of your API...
an array	List, Collection (as is), a Java array (copied)
a table	Map

import java.util.ArrayList;

dyn list = new ArrayList();
list.add(3); list.add(1); list.add(2);
list.sort((a, b) -> a - b);                 // a lambda as a Comparator
println(list);                              // [1, 2, 3]
println(String.join("-", ["a", "b"]));      // a-b - an array as an Iterable
new Thread(() -> println("run")).run();     // a lambda as a Runnable

Java arrays

dyn ints = new int[3];
dyn names = new String[]{"x", "y"};
println(names[1], names.length, type(ints));   // y 2 int[]

Exceptions

A Java exception reaches catch as the exception object:

try {
    Integer.parseInt("x");
} catch (e) {
    println(isa(e, NumberFormatException), e.getMessage());   // true For input string: "x"
}

What values look like from Java

Jumper	Java
null, numbers, booleans, strings	null, Integer / Long / Double, Boolean, String
array	me.padej.jumper.runtime.JArray (a java.util.List)
table, object of a Jumper class	me.padej.jumper.runtime.JTable (get, put, keys, asMap())
function	me.padej.jumper.runtime.JFunction (call(Object[]))

Next: Embedding.