/Users/parrt/antlr/code/antlr/main/runtime/Java/src/main/java/org/antlr/runtime/misc/FastQueue.java

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/*
 [The "BSD license"]
 Copyright (c) 2005-2009 Terence Parr
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
     documentation and/or other materials provided with the distribution.
 3. The name of the author may not be used to endorse or promote products
     derived from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 */
package org.antlr.runtime.misc;

import java.util.List;
import java.util.ArrayList;
import java.util.NoSuchElementException;

public class FastQueue<T> {
    protected List<T> data = new ArrayList<T>();
    protected int p = 0;
        protected int range = -1; // how deep have we gone?     

    public void reset() { clear(); }
    public void clear() { p = 0; data.clear(); }

    public T remove() {
        T o = elementAt(0);
        p++;
        // have we hit end of buffer?
        if ( p == data.size() ) {
            // if so, it's an opportunity to start filling at index 0 again
            clear(); // size goes to 0, but retains memory
        }
        return o;
    }

    public void add(T o) { data.add(o); }

    public int size() { return data.size() - p; }

        public int range() { return range; }

    public T head() { return elementAt(0); }

    public T elementAt(int i) {
                int absIndex = p + i;
                if ( absIndex >= data.size() ) {
            throw new NoSuchElementException("queue index "+ absIndex +" > last index "+(data.size()-1));
        }
        if ( absIndex < 0 ) {
            throw new NoSuchElementException("queue index "+ absIndex +" < 0");
        }
                if ( absIndex>range ) range = absIndex;
        return data.get(absIndex);
    }

    public String toString() {
        StringBuffer buf = new StringBuffer();
        int n = size();
        for (int i=0; i<n; i++) {
            buf.append(elementAt(i));
            if ( (i+1)<n ) buf.append(" ");
        }
        return buf.toString();
    }
}

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