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Set and Retrieve a Script Engine's State
A script engine has state that can be set by a Java program, accessed and manipulated by a script, and retrieved by the Java program. The program sets this state by invoking ScriptEngine's public void put(String key, Object value) method, where key typically identifies a scripting language variable and value provides the variable's value. Similarly, a Java program invokes ScriptEngine's public Object get(String key) method to retrieve the state value. Listing 3 describes an application that demonstrates these methods.
Listing 3: ScriptDemo3.java
// ScriptDemo3.java
import javax.script.*;
public class ScriptDemo3
{
public static void main (String [] args) throws ScriptException
{
// Create a ScriptEngineManager that discovers all script engine
// factories (and their associated script engines) that are visible to
// the current thread's classloader.
ScriptEngineManager manager = new ScriptEngineManager ();
// Obtain a ScriptEngine that supports the JavaScript short name.
ScriptEngine engine = manager.getEngineByName ("JavaScript");
// Initialize the age script variable to 85 (an Integer).
engine.put ("age", 85);
// Evaluate a script that determines if a person can obtain an amount to
// deduct from their taxable income based on age.
engine.eval ("var ageAmount = 0.0; if (age >= 65) ageAmount += 6000;");
// Retrieve the ageAmount script variable (a Double) and output its
// value.
System.out.println ("ageAmount = " + engine.get ("ageAmount"));
}
}
ScriptDemo3 creates the following output:
ageAmount = 6000.0