org.eclipse.jdt.internal.compiler.util.SimpleLookupTable.java Source code

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Here is the source code for org.eclipse.jdt.internal.compiler.util.SimpleLookupTable.java

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/*******************************************************************************
 * Copyright (c) 2000, 2009 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.compiler.util;

/**
 * A simple lookup table is a non-synchronized Hashtable, whose keys
 * and values are Objects. It also uses linear probing to resolve collisions
 * rather than a linked list of hash table entries.
 */
public final class SimpleLookupTable implements Cloneable {

    // to avoid using Enumerations, walk the individual tables skipping nulls
    public Object[] keyTable;
    public Object[] valueTable;
    public int elementSize; // number of elements in the table
    public int threshold;

    public SimpleLookupTable() {
        this(13);
    }

    public SimpleLookupTable(int size) {
        this.elementSize = 0;
        this.threshold = size; // size represents the expected number of elements
        int extraRoom = (int) (size * 1.5f);
        if (this.threshold == extraRoom)
            extraRoom++;
        this.keyTable = new Object[extraRoom];
        this.valueTable = new Object[extraRoom];
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        SimpleLookupTable result = (SimpleLookupTable) super.clone();
        result.elementSize = this.elementSize;
        result.threshold = this.threshold;

        int length = this.keyTable.length;
        result.keyTable = new Object[length];
        System.arraycopy(this.keyTable, 0, result.keyTable, 0, length);

        length = this.valueTable.length;
        result.valueTable = new Object[length];
        System.arraycopy(this.valueTable, 0, result.valueTable, 0, length);
        return result;
    }

    public boolean containsKey(Object key) {
        int length = this.keyTable.length;
        int index = (key.hashCode() & 0x7FFFFFFF) % length;
        Object currentKey;
        while ((currentKey = this.keyTable[index]) != null) {
            if (currentKey.equals(key))
                return true;
            if (++index == length)
                index = 0;
        }
        return false;
    }

    public Object get(Object key) {
        int length = this.keyTable.length;
        int index = (key.hashCode() & 0x7FFFFFFF) % length;
        Object currentKey;
        while ((currentKey = this.keyTable[index]) != null) {
            if (currentKey.equals(key))
                return this.valueTable[index];
            if (++index == length)
                index = 0;
        }
        return null;
    }

    public Object getKey(Object key) {
        int length = this.keyTable.length;
        int index = (key.hashCode() & 0x7FFFFFFF) % length;
        Object currentKey;
        while ((currentKey = this.keyTable[index]) != null) {
            if (currentKey.equals(key))
                return currentKey;
            if (++index == length)
                index = 0;
        }
        return key;
    }

    public Object keyForValue(Object valueToMatch) {
        if (valueToMatch != null)
            for (int i = 0, l = this.keyTable.length; i < l; i++)
                if (this.keyTable[i] != null && valueToMatch.equals(this.valueTable[i]))
                    return this.keyTable[i];
        return null;
    }

    public Object put(Object key, Object value) {
        int length = this.keyTable.length;
        int index = (key.hashCode() & 0x7FFFFFFF) % length;
        Object currentKey;
        while ((currentKey = this.keyTable[index]) != null) {
            if (currentKey.equals(key))
                return this.valueTable[index] = value;
            if (++index == length)
                index = 0;
        }
        this.keyTable[index] = key;
        this.valueTable[index] = value;

        // assumes the threshold is never equal to the size of the table
        if (++this.elementSize > this.threshold)
            rehash();
        return value;
    }

    public Object removeKey(Object key) {
        int length = this.keyTable.length;
        int index = (key.hashCode() & 0x7FFFFFFF) % length;
        Object currentKey;
        while ((currentKey = this.keyTable[index]) != null) {
            if (currentKey.equals(key)) {
                this.elementSize--;
                Object oldValue = this.valueTable[index];
                this.keyTable[index] = null;
                this.valueTable[index] = null;
                if (this.keyTable[index + 1 == length ? 0 : index + 1] != null)
                    rehash(); // only needed if a possible collision existed
                return oldValue;
            }
            if (++index == length)
                index = 0;
        }
        return null;
    }

    public void removeValue(Object valueToRemove) {
        boolean rehash = false;
        for (int i = 0, l = this.valueTable.length; i < l; i++) {
            Object value = this.valueTable[i];
            if (value != null && value.equals(valueToRemove)) {
                this.elementSize--;
                this.keyTable[i] = null;
                this.valueTable[i] = null;
                if (!rehash && this.keyTable[i + 1 == l ? 0 : i + 1] != null)
                    rehash = true; // only needed if a possible collision existed
            }
        }
        if (rehash)
            rehash();
    }

    private void rehash() {
        SimpleLookupTable newLookupTable = new SimpleLookupTable(this.elementSize * 2); // double the number of expected elements
        Object currentKey;
        for (int i = this.keyTable.length; --i >= 0;)
            if ((currentKey = this.keyTable[i]) != null)
                newLookupTable.put(currentKey, this.valueTable[i]);

        this.keyTable = newLookupTable.keyTable;
        this.valueTable = newLookupTable.valueTable;
        this.elementSize = newLookupTable.elementSize;
        this.threshold = newLookupTable.threshold;
    }

    @Override
    public String toString() {
        String s = ""; //$NON-NLS-1$
        Object object;
        for (int i = 0, l = this.valueTable.length; i < l; i++)
            if ((object = this.valueTable[i]) != null)
                s += this.keyTable[i].toString() + " -> " + object.toString() + "\n"; //$NON-NLS-2$ //$NON-NLS-1$
        return s;
    }
}