CircularArrayList.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.android.tools.chartlib;

import com.android.annotations.NonNull;

import java.util.AbstractList;

/**
 * A circular list that is backed by an array. Once the list reaches the allocated size, it will
 * start reusing the oldest entry.
 */
class CircularArrayList<T> extends AbstractList<T> {

    @NonNull
    private final T[] mData;

    private int mSize;

    private int mStart;

    CircularArrayList(int alloc) {
        mData = (T[]) new Object[alloc];
        mSize = 0;
        mStart = 0;
    }

    @Override
    public T get(int i) {
        if (i < 0 || i >= mSize) {
            throw new IndexOutOfBoundsException();
        }
        return mData[(mStart + i) % mSize];
    }

    @Override
    public boolean add(T t) {
        if (mSize == mData.length) {
            mData[mStart] = t;
            mStart = (mStart + 1) % mSize;
        } else {
            mData[mSize] = t;
            mSize++;
        }
        return true;
    }

    @Override
    public int size() {
        return mSize;
    }

    @Override
    public void clear() {
        mStart = 0;
        mSize = 0;
    }
}