/*
 * @(#)AbstractScriptEngine.java	1.5 06/06/19 20:54:01
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTAIL. Use is subject to license terms.
 */

package javax.script;
import java.io.Reader;
import java.util.Map;
import java.util.Iterator;

/**
 * Provides a standard implementation for several of the variants of the <code>eval</code>
 * method.
 * <br><br>
 * <code><b>eval(Reader)</b></code><p><code><b>eval(String)</b></code><p>
 * <code><b>eval(String, Bindings)</b></code><p><code><b>eval(Reader, Bindings)</b></code>
 * <br><br> are implemented using the abstract methods
 * <br><br>
 * <code><b>eval(Reader,ScriptContext)</b></code> or
 * <code><b>eval(String, ScriptContext)</b></code>
 * <br><br>
 * with a <code>SimpleScriptContext</code>.
 * <br><br>
 * A <code>SimpleScriptContext</code> is used as the default <code>ScriptContext</code>
 * of the <code>AbstractScriptEngine</code>..
 *
 * @author Mike Grogan
 * @version 1.0
 * @since 1.6
 */
public abstract class AbstractScriptEngine  implements ScriptEngine {
    
    /**
     * The default <code>ScriptContext</code> of this <code>AbstractScriptEngine</code>.
     */
    
    protected ScriptContext context;
    
    /**
     * Creates a new instance of AbstractScriptEngine using a <code>SimpleScriptContext</code>
     * as its default <code>ScriptContext</code>.
     */
    public AbstractScriptEngine() {
        
        context = new SimpleScriptContext();
        
    }
    
    /**
     * Creates a new instance using the specified <code>Bindings</code> as the
     * <code>ENGINE_SCOPE</code> <code>Bindings</code> in the protected <code>context</code> field.
     *
     * @param n The specified <code>Bindings</code>.
     * @throws NullPointerException if n is null.
     */
    public AbstractScriptEngine(Bindings n) {
        
        this();
        if (n == null) { 
            throw new NullPointerException("n is null");
        }
        context.setBindings(n, ScriptContext.ENGINE_SCOPE);
    }
    
    /**
     * Sets the value of the protected <code>context</code> field to the specified
     * <code>ScriptContext</code>.
     *
     * @param ctxt The specified <code>ScriptContext</code>.
     * @throws NullPointerException if ctxt is null.
     */
    public void setContext(ScriptContext ctxt) {
        if (ctxt == null) {
            throw new NullPointerException("null context");
        }
        context = ctxt;
    }
    
    /**
     * Returns the value of the protected <code>context</code> field.
     *
     * @return The value of the protected <code>context</code> field.
     */
    public ScriptContext getContext() {
        return context;
    }
    
    /**
     * Returns the <code>Bindings</code> with the specified scope value in
     * the protected <code>context</code> field.
     *
     * @param scope The specified scope
     *
     * @return The corresponding <code>Bindings</code>.
     *
     * @throws IllegalArgumentException if the value of scope is
     * invalid for the type the protected <code>context</code> field.
     */