Java example source code file (ConstantData.java)

This example Java source code file (ConstantData.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, arraywrapper, assertionerror, class, constantdata, hashmap, integer, list, map, object, override, string, util

The ConstantData.java Java example source code

/*
 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package jdk.nashorn.internal.codegen;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Manages constants needed by code generation.  Objects are maintained in an
 * interning maps to remove duplicates.
 */
class ConstantData {
    /** Constant table. */
    final List<Object> constants;

    /** Constant table string interning map. */
    final Map<String, Integer> stringMap;

    /** Constant table object interning map. */
    final Map<Object, Integer> objectMap;

    private static class ArrayWrapper {
        private final Object array;
        private final int    hashCode;

        public ArrayWrapper(final Object array) {
            this.array    = array;
            this.hashCode = calcHashCode();
        }

        /**
         * Calculate a shallow hashcode for the array.
         * @return Hashcode with elements factored in.
         */
        private int calcHashCode() {
            final Class<?> cls = array.getClass();

            if (cls == Object[].class) {
                return Arrays.hashCode((Object[])array);
            } else if (cls == double[].class) {
                return Arrays.hashCode((double[])array);
            } if (cls == long[].class) {
                return Arrays.hashCode((long[])array);
            } if (cls == int[].class) {
                return Arrays.hashCode((int[])array);
            }

            throw new AssertionError("ConstantData doesn't support " + cls);
        }

        @Override
        public boolean equals(final Object other) {
            if (!(other instanceof ArrayWrapper)) {
                return false;
            }

            final Object otherArray = ((ArrayWrapper)other).array;

            if (array == otherArray) {
                return true;
            }

            final Class<?> cls = array.getClass();

            if (cls == otherArray.getClass()) {
                if (cls == Object[].class) {
                    return Arrays.equals((Object[])array, (Object[])otherArray);
                } else if (cls == double[].class) {
                    return Arrays.equals((double[])array, (double[])otherArray);
                } else if (cls == long[].class) {
                    return Arrays.equals((long[])array, (long[])otherArray);
                } else if (cls == int[].class) {
                    return Arrays.equals((int[])array, (int[])otherArray);
                }
            }

            return false;
        }

        @Override
        public int hashCode() {
            return hashCode;
        }
    }

    /**
     * Constructor
     */
    ConstantData() {
        this.constants = new ArrayList<>();
        this.stringMap = new HashMap<>();
        this.objectMap = new HashMap<>();
    }

    /**
     * Add a string to the constant data
     *
     * @param string the string to add
     * @return the index in the constant pool that the string was given
     */
    public int add(final String string) {
        final Integer value = stringMap.get(string);

        if (value != null) {
            return value.intValue();
        }

        constants.add(string);
        final int index = constants.size() - 1;
        stringMap.put(string, index);

        return index;
    }

    /**
     * Add an object to the constant data
     *
     * @param object the string to add
     * @return the index in the constant pool that the object was given
     */
    public int add(final Object object) {
        final Object  entry = object.getClass().isArray() ? new ArrayWrapper(object) : object;
        final Integer value = objectMap.get(entry);

        if (value != null) {
            return value.intValue();
        }

        constants.add(object);
        final int index = constants.size() - 1;
        objectMap.put(entry, index);

        return index;
    }

    Object[] toArray() {
        return constants.toArray();
    }
}