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# Jep Java

- Introduction
- Basic Usage
- Variables
- Data types
- Operators
- Functions
- Custom Functions
- BigDecimal
- Modules
- Printing
- FAQ
- Migration
- Version History

# Advanced Features

- Manipulating Expressions
- Components
- Configurable Parser
- Serialization
- Threads
- Localization
- Grammar
- Other advanced features
- Use of Design Patterns in Jep

# Serialization

Starting with Jep 3.1, parsed expressions, the main Jep class, and its subcomponents are all serializable. This allows persistent storage and transfer between applications. Issues regarding threads and the use of multiple Jep instances are also discussed in this section.

## What needs to be serialized?

Depending on your needs you may choose from three different serialization options:

- Expressions only: If the source and destination have the same set up for Jep, with the same set of functions and operators then this form will take the minimum size.
- VariableTable and expressions: this will also save the values of variables
- Full serialization: serializes the Jep instance, together with its configuration and settings.

## Serializing an expression

The Node class itself is not serializable. Instead, a wrapper class com.singularsys.jep.walkers.SerializableExpression is used to provide a compact serializable representation of a node. The class is constructed using `new SerializedExpression(Node n)` and the `Node toNode(Jep j)` method is used to extract the node in the context of a given Jep instance.

To serialize use:

    //  Set-up jep
    Jep j = new Jep();

    // create an ObjectOutputStream
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);

    // parse an expression
    Node n = j.parse("1+cos(2 th)");

    // Create a SerializableExpression
    SerializableExpression se = new SerializableExpression(n);

    // write the SerializedExpression
    oos.writeObject(se);
    oos.close();

    // extract the bytes
    byte bytes[] = baos.toByteArray();

To deserialize the expression use:

    //  Set-up jep
    Jep j2 = new Jep();

    // Create an ObjectInputStream from the set of bytes
    ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
    ObjectInputStream ois = new ObjectInputStream(bais);

    // Deserialize the SerializableExpression
    SerializableExpression se2 = (SerializableExpression) ois.readObject();

    // Create a node
    Node n2 = se2.toNode(j2);
    ois.close();

Alternatively, the serialized expression could be written to a file

    ....
    File f = new File(....);
    FileOutputStream fos = new FileOutputStream(f);
    ObjectOutputStream oos = new ObjectOutputStream(fos);

    // write objects
    oos.writeObject(se);
    oos.close();

    FileInputStream fis = new FileInputStream(f);
    ObjectInputStream ois = new ObjectInputStream(fis);

    // read objects
    SerializableExpression se2 = (SerializableExpression) ois.readObject();
    ois.close();

### Serializing the VariableTable and an expression

If you wish to serialize the values of variables for later use, then the VariableTable can be serialized. Again this method assumes the same version and configuration of the Jep instances.

    Jep j = new Jep();

    // Setup the ObjectOutputStream
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);

    // Serialize the VariableTable
    oos.writeObject(j.getVariableTable());

    // Serialize the expression
    Node n = j.parse("a+cos(2 th)");
    SerializableExpression se = new SerializableExpression(n);
    oos.writeObject(se);

    oos.close();
    byte bytes[] = baos.toByteArray();

To deserialize

    //  Set-up jep
    Jep j2 = new Jep();

    // Create an ObjectInputStream
    ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
    ObjectInputStream ois = new ObjectInputStream(bais);

    // Deserialize the SymbolTable
    VariableTable vt2 = (VariableTable) ois.readObject();

    // Set the SymbolTable as that used by the jep instance
    j2.setComponent(vt2);

    // Deserialize the expression
    SerializableExpression se2 = (SerializableExpression) ois.readObject();
    Node n2 = se2.toNode(j2);
    ois.close();

### Serializing the Jep instance

The Jep class and all its components are serializable, meaning that the configuration of the Jep instance can be stored. This includes the full set of variables, functions, operators, and various settings. If the ConfigurableParser is used, then its configuration is also stored. Note that changes made to the standard JavaCC parser are not recorded.

A typical setup will take 7KB with the standard parser and 12KB with the configurable parser.

    Jep j = new Jep();

    // Setup the ObjectOutputStream
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);

    // Serialize the VariableTable
    oos.writeObject(j);

    // Serialize the expression
    Node n = j.parse("a+cos(2 th)");
    SerializableExpression se = new SerializableExpression(n);
    oos.writeObject(se);

    oos.close();
    byte bytes[] = baos.toByteArray();

To deserialize

    // Create an ObjectInputStream from the set of bytes
    ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
    ObjectInputStream ois = new ObjectInputStream(bais);

    // Deserialize the Jep instance
    Jep j2 = (Jep) ois.readObject();

    // Deserialize the expression
    SerializableExpression se2 = (SerializableExpression) ois.readObject();
    Node n2 = se2.toNode(j2);
    ois.close();

### Importing equations

The SerializedExpression class can also be used to produce copies of a node without having to serialize and deserialize.

    // Create first instance
    Jep j = new Jep();

    // Parse equation using first instance
    Node n = j.parse("a+cos(2 th)");

    // Create a SerializableExpression
    SerializableExpression se = new SerializableExpression(n);

    // Create second instance
    Jep j2 = new Jep();

    // Import expression into second instance
    Node n2 = se.toNode(j2);

An alternative method is to use an ImportationVisitor which is a bit faster but cannot handle as large equations.