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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.

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/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.javascript.engine;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import javax.script.ScriptContext;
import org.mozilla.javascript.Context;
import org.mozilla.javascript.Function;
import org.mozilla.javascript.ScriptRuntime;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;

/**
 * This class defines the following built-in functions for the RhinoScriptEngine.
 *
 * 
 *   print(arg, arg, ...): Write each argument, concatenated to the ScriptEngine's "standard
 *       output" as a string.
 * 
 */
public class Builtins {

    static final Object BUILTIN_KEY = new Object();

    private Writer stdout;

    void register(Context cx, ScriptableObject scope, ScriptContext sc) {
        if (sc.getWriter() == null) {
            stdout = new OutputStreamWriter(System.out);
        } else {
            stdout = sc.getWriter();
        }

        scope.defineFunctionProperties(
                new String[] {"print"},
                Builtins.class,
                ScriptableObject.PERMANENT | ScriptableObject.DONTENUM);
    }

    public static void print(Context cx, Scriptable thisObj, Object[] args, Function f)
            throws IOException {
        Builtins self = getSelf(thisObj);
        for (Object arg : args) {
            self.stdout.write(ScriptRuntime.toString(arg));
        }
        self.stdout.write('\n');
        // ref bug https://github.com/mozilla/rhino/issues/1356
        self.stdout.flush();
    }

    private static Builtins getSelf(Scriptable scope) {
        // Since this class is invoked as a set of anonymous functions, "this"
        // in JavaScript does not point to "this" in Java. We set a key on the
        // top-level scope to address this.
        return (Builtins) ScriptableObject.getTopScopeValue(scope, BUILTIN_KEY);
    }
}