User guide

Work in progress... To introduce Zaluum at this Preview stage, it will be assumed that you have a basic knowledge of Java. Please refer to the java tutorial, to refresh the basic concepts.

About boxes

Boxes are the basic building blocks of Zaluum.

Box anatomy

Boxes represent operations on data. They operate on the data arriving by the wires attached to them. The points where you can attach a wire to a box are called ports.

Ports at the left side of a box are input ports. Ports at the right side, output ports. A box performs some operation to the inputs and, optionally, its internal state to produce one or more outputs.

Composite boxes can make use of the shift ports. A Shift port holds the last value it's been written and can be read and written multiple times from inside the box they are assigned.

Shift ports are showed as a port connection in both sides of the composite box. Each port connection has one terminal inside the box and another one outside. So each shift port has a total of 4 terminals.

When a composite box starts to execute, the initial value of the shift port is taken from the outside terminal of the left connection, like an input port. On each iteration, the port value is updated with the inside connection at the right side. Finally the other boxes can read the value set in the last iteration on the right terminal of the right connection.

Some boxes

Execution order

The execution order of the boxes is calculated by the platform based on the rule that a box can only be executed when all the boxes that provide its inputs have already been executed. This means that no cycles can be present in a Zaluum diagram, since no solution could be found.

The execution order of two boxes with no data dependency is undefined and can potentially be executed in parallel.


The data dependency between boxes must form a Direct Acyclic Graph (DAG). The execution order is a Topologic Order on this graph.

Wires and data types

Each port has a definite data type. The types in Zaluum are the types available in Java: Class (or interface), Array or primitive type.

You can connect an output port to multiple inputs but an input can only have one connection. An unconnected input defaults to 0 or null .

You can create connections between an input and an output only if they have compatible types. Type compatibility follows the rules of java for type conversion and promotion, detailed in the Java Language Specification . In summary two types are compatible if:

  • They are the same
  • They are primitive type and you can convert the source type into the target type with no loss. A byte into an int but not int to byte.
  • The source type is a subclass or implements the interface of the target type.

Primitive types can be boxed and unboxed before applying the above rules.

NOTE Java 5.0 generics are not yet supported.

Box properties

Inputs and outputs apart, boxes have also properties.

There are 3 properties shared across all types of boxes

  • *Name An unique name in the class. Must be a valid Java identifier (start with letter, no spaces, no symbols)
  • *Label An optional string that is shown in the diagram next to the box
  • *GUI Label An optional string shown in the GUI next to the widget
  • *Type The type of the box

Depending on the type of the box, there can be more properties added to box. Please refer to the box types guide.

Finally, the box instance type adds the JavaBeans properties of the class of the box.

Classes and packages

Each type has a color and line style in Zaluum, the Java primitive types are:
boolean red
byte cyan
char green
short light blue
int blue
long dark blue
float yellow
double orange

About Eclipse

The Zaluum support in Eclipse is nearly transparent to the user. There are a few concepts worth knowing.

Zaluum projects

The Zaluum source files must reside in source folder of an Eclipse project with both Java nature and Zaluum nature enabled. This is a Zaluum Project. You can create a Zaluum project by:
  • Creating a Zaluum Project with File→New→Zaluum Project
  • Adding the Zaluum Nature to a Java Project. Right click on the project Configure→Convert to Zaluum Project

When you create a Zaluum Project the needed Zaluum Library Container is added to the classpath.

Views and perspectives

When you switch to a Zaluum Project, the Zaluum Perspective is automatically enabled. It contains the Zaluum Properties view and the Zaluum Palette view. The Zaluum Properties view is required to edit Zaluum files, but the palette can also be reached by right-clicking a blank space in an open Zaluum File.

NOTE It is very useful to have the Problems view in sight while editing Zaluum Files. You can double click the error to go to the source of the problem.

Running a Zaluum Project

You can run a Zaluum file in a simple runtime framework selecting the desired main Zaluum class, right clicking and select Run as...→Zaluum Application. Note that to launch a Zaluum file in this mode it cannot contain any input ports.

As Zaluum projects are Java projects, so you can create a class with a main and call the Zaluum files from there.

GUI editor

Zaluum can also create a graphical interface for your box. Press F6 or the GUI button on the toolbar to open it. The GUI editor changes the setBounds property of the boxes inside.

If you remove the Zaluum Library Container by accident, you can reenable it doing the following: Right click on the project Build Path→Add Libraries and select Zaluum Library Container

NOTE When you create a Zaluum project, the required classpath libraries are set up automatically, so you don't need to worry about this.

Compilation is done automatically if Project→Build automatically is checked.
Refactorings are not yet implemented, and some functions of Eclipse Java support may not work in the presence of Zaluum files.

Basic boxes

They can be found in the org.zaluum.op package of the palette.

Name Inputs Outputs Description
Literal expression
0 inputs 1 output
The narrowest type that can hold the parsed data.

Creates values from a string. Use it to insert constant numbers or strings into your dataflow.

The property literal is parsed and converted it into a value with the following rules:

  • true and false are converted to boolean
  • If the literal ends with the letter f or F it's converted to a float
  • If the literal ends with the letter l or L it's converted to a long
  • If the literal starts and ends with double quotes " its converted to a String (double quotes not included)
  • Else it's parsed as an integer. The type is the smallest that can hold the value: byte,short or int
  • If failed to parse as an integer. It's parsed like a double.
  • Finally if all fails, it's interpreted as a String
Arithmetic operations
  • Sum
  • Substraction
  • Multiplication
  • Division
  • Remainder
2 inputs
int , long , float or double
1 output
Its type is the wider type of the two inputs.
Perform numeric operations on incoming data. You can operate with smaller primitive types byte or char with the automatic cast to int.
1 inputs
int , long , float or double
1 output
The same as the input.
Changes the sign of the input. Equivalent to multiply by -1
Bitwise operations
  • And
  • Or
  • Xor
  • Not
2 inputs
boolean, int or long (Not has only 1 input)
1 output
boolean, int or long
Performs the operation bitwise on numeric types or applies the logic to the boolean data.
Shift operations
  • Shift left
  • Shift right
  • Unsigned rotate right
2 inputs
toShift: int or long
shift distance: int
1 output
int or long
Shift and rotates like shift operators in Java TODO link
Equality testing
  • Equals
  • Not equals
2 inputs
Any type
1 output
Compares two primitives, or two objects for equality (by reference) TODO
Numeric comparison
  • Less than Lt <
  • Less or equal than Le
  • Greater than Gt >
  • Greater or equal than Ge
2 inputs
Any primitive numeric type.
1 output
Performs the comparison and returns the result.

Composite boxes

Name Inputs Outputs Description
While box
  • N user ports: input or shift
  • 1 boolean condition output. If true the body is executed again.
  • N user ports: output or shift
Executes the inner boxes in their order one time. If the cond port is true, they are executed again, with the values of the shift ports assigned in the last iteration.
If box
  • 1 boolean condition port
  • N user ports
  • N user ports
If box has two pages, and each one can contain inner boxes. Page selected as T by switch is executed if the cond port is true, the F page if false.

Object boxes

Object boxes operate with object oriented logic, similar to the same concepts in Java.

Name Inputs Outputs Parameters Description
Box instance
  • N inputs. The number an type of the parameters of the selected #Method
  • Zero or one. The return value of the selected #Method
  • N outputs. The selected #Fields or the fields annotated with @org.zaluum.annotation.Out
  • #Class The name of the class to create
  • #Method The name and arity of candidate methods
  • #Fields The names of the fields to be added as outputs
  • #Constructor types The types of the parameters of the constructor to be used
  • #Constructor values The values of the parameters of the constructor
  • #Script An optional JavaScript to be executed after the object creation
  • N properties. All the JavaBean properties of the class defined with a getter and setter method with a type that can be parsed as a literal.

This box type creates an instance of a class box. It does it in a series of steps:

  1. Creates an instance of the class Class using the constructor that matches the arity (number of parameters) and types of #Constructor types .

    To invoke the constructor it parses the values #Constructor values using the #Constructor types

    If no constructor is specified it uses the public default constructor (public with no parameters).

    and stores it in an internal field. It uses the constructor
  2. The newly created box is stored in an internal field of the class being defined.
  3. After the creation of the object, the contents of #Script are evaluated as JavaScript. This can be useful for some widget setup tools to configure the recently created object.

The behavior of the box is determined by the properties #Method and #Fields .

#Method chooses the name and arity of the candidate methods to be invoked. The actual method invoked will be determined among the overloaded methods by the compatibility of the incoming wires. If no #Method is specified, the ones with an @Apply annotation are selected as candidates.

The inputs will be:

  • The parameters of the choosen method.

The outputs will be:

  • One or zero ports: The return value of the method invocation. Zero if void
  • Plus Zero or more: The values of the #Fields after the method invocation.
This box type is likely to change before v1.0
This reference None
  • 1 output.
    The this reference. The type is the class in which this box is instanced.

Returns the current instance of the class in which it appears. Like the Java this .

Type cast
  • objectIn an object or primitive value. Any type.
  • objectOut The value objectIn casted to type #Class
  • #Class The class or primitive type to cast to.
Converts one type into another. The rules are the same as Java.
Method invocation
  • objectIn: The object on which invoke the method
  • N ports: The parameters of the method to be invoked on objectIn
  • objectOut The same object as objectIn. (For chaining)
  • Zero or One: The return value of the method. (Zero if void)
#Method The name and arity of the method to be invoked on the object objectIn

Invokes the method that matches the name and arity of #Method and the types of the incoming wires to the N input ports. The result of the invocation is put on the output

The objectIn reference is copied to objectOut

Static method invocation
  • N inputs. The parameters of the static method invoked.
  • 0 or 1 outputs. The result of the invocation
  • #Class The class containing the static method
  • #Method The name and arity of the method to be invoked
Invokes the static method on the #Class that matches the name and arity of #Method and the types of the incoming wires to the N input ports. The result of the invocation is put on the output.
Field access
  • objectIn The object having the field.
  • 1 input - If wired it sets the value of the field.
  • objectOut The objectIn reference
  • 1 output - The value of the field
#Field The name of the accessed field.

If the input is wired, it sets the field named #Field of objectIn to the incoming value. The output is the value of the field.

The objectIn reference is copied to objectOut

Static field access
  • 1 input. If wired it sets the value of the field.
  • 0 or 1 outputs. The value of the field
  • #Class The class containing the static field
  • #Field The name of the static field accessed.

If the input is wired, it sets the static field named #Field of the class #Class to the incoming value. The output is the value of the static field.

New object
  • N inputs. The constructor parameters
  • 1 output. The new object of type #Class
  • #Class The class to be instanced.
  • #Constructor The arity of the constructor
Creates a new object using a constructor matching the arity of #Constructor and the parameter types of the incoming wires. The result is a new object of class #Class.
Array access
  • objectIn The array being accessed
  • index an int representing the 0-based index to access
  • One input. If wired it sets the value of the array at index index
  • objectOut The array objectIn
  • one output. The value of the array at index index
Accesses the array at index index. If the input is wired it sets its value.
Array compose
  • #Size number of inputs of type #Class.
  • 1 output. The created array of type #Class and length #Size.
  • #Class the class or primitive type of the array being created
  • #Size the number of inputs (size of the array)
Creates a new array of type #Class and size #Size. The values of the array are those wired to each position.
New array #Array Dimensions number of inputs representing the size of each dimension (ints)
  • array The newly created array.
  • #Class The type of the array.
  • #Array Dimensions The number of dimensions of the array

Creates an array of type #Class of #Array Dimensions . The size of each dimension is assigned by the inputs.

For example #Array Dimensions =2 and #Class = int would be equivalent to the Java code: new int[a][b](); . Being a and b the input ports.

Using Java from Zaluum

Method overloading

There are some box types that require you to specify a method to invoke in their properties. In Java, a method name can be overloaded: methods can share name in the same class as long as they have different signatures i.e. have distinguishable parameters, by type and/or by number(arity).

For example:

class Foo {
	public void bar(int a, int b) {
	public long bar(int a, long b) {
		return a-b;
	public int bar() {
		return 0;

When a box requires a method, you need to specify a name and the number of parameters taken (arity). In the example if we select name bar with arity 2, the box will show 2 input ports. The method to be called (int,int) or (int,long) will depend on the wires we connect to its inputs. If we connect two ints, the first will be called; if we connect (int,long), the second. There will not be an output port in the first case, and a long one will appear in the second.

Zaluum matches the best method to call according the Java rules of method invocation. If there is any ambiguity an error is shown. In the example, if no input is connected the method to invoke is ambigous, and an error is shown.

TIP Because of method overloading, some boxes can change its outputs when connected, depending on the type of the wires we attach to it.

The palette

The Zaluum palette is composed of:

  • Tools to create ports
  • Simple Zaluum box types
  • Templates

The simple Zaluum box types are the basic building blocks of all Zaluum files, and all the simple types are listed in the section Types of boxes. They are equivalent to the basic syntax of a textual language.

The Templates are simple Zaluum box types with some properties pre-set. They are useful because they let you add boxes faster. Template entries to the palette come from the following sources:

  • Every Zaluum file creates a Template of Box Instance with #Class set to the Zaluum file, so you can instantiate Zaluum boxes easily.
  • Java classes annotated with @org.zaluum.annotation.Box create a Template of Box Instance with #Class set to the Java class. You can instantiate Java classes easily if they have been annotated with Box.
  • Java public static methods annotated with @org.zaluum.annotation.Box, that reside in any Java class annotated with @org.zaluum.annotation.StaticBox create a Template of Static Method Invocation with #Class set to the enclosing class and #Method selecting the annotated method. This way you can turn static methods into boxes easily.
  • All the classpath roots (your source and library jars) are scanned for the file /META-INF/zaluum.xml. This file may contain additional template entries and is described in section XXX.


The icon shown for a box in the diagram view and in the palette is determined in the following order:

  • If an image override in a META-INF/zaluum.xml file exists for the box, it's chosen. See XXX.
  • If a file with .png extension, in the same package and with the same name of the box meant to override is present, it's chosen.
  • A fallback icon is generated with the name of the class.
An icon for a package can also be defined by putting a package.png in the package directory.

Swing widgets

When using a Box Instance with a Java class, if this Java class extends java.awt.Component , the box is considered visual and the widget is shown in the GUI view. The position and size assigned to the widget to the setBounds method of java.awt.Component .

Zaluum from Java

Java view of Zaluum file

A Zaluum file, viewed from Java, is equivalent to the following:

  • A public class named as the file (without the .zaluum) in the package XXX.
  • The class contains a public execution method that runs the dataflow:
    • The name of the execution method is the name of the first output port in lexicographic ordering or "run" if no output port is present.
    • The return value of the method is the value of this same port, or void if none is present.
    • The parameters of the method are the input ports of the Zaluum file in lexicographic ordering.
    • For the second and following output ports, a public field with matching type and name is generated for each one. After the invocation of the execution method the values are updated with the results of the computation.
    • The boxes of type Box Instance, are stored as a public field of type #Class with field name *Name. XXX
  • If the Zaluum file is visual (contains a visual widget), the class extends javax.swing.JFrame. The property getPreferredSize() is set to the size of the canvas of the GUI view and the widgets are added to it with a null LayoutManager, each with the getBounds() property set.

To be documented

  • Annotations and palette.xml
  • Zaluum Constructor and Initialization
  • Configuration wizards
  • Port naming internals
  • Scripting
  • Javadoc integration
  • Building with ant