安全的自增类

java中一个计数器如果超过MAX_VALUE再自增会如何？很可能会是负数。下面是一个安全的自增类

 

/*

 * Copyright 1999-2011 Alibaba Group.

 *  

 * 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.alibaba.dubbo.common.utils;



import java.util.concurrent.atomic.AtomicInteger;



/**

 * AtomicPositiveInteger

 * 

 * @author william.liangf

 * @author ding.lid

 */

public class AtomicPositiveInteger extends Number {

    

    private static final long serialVersionUID = -3038533876489105940L;

    

    private final AtomicInteger i;

    

    public AtomicPositiveInteger() {

        i = new AtomicInteger();

    }

    

    public AtomicPositiveInteger(int initialValue) {

        i = new AtomicInteger(initialValue);

    }



    public final int getAndIncrement() {

        for (;;) {

            int current = i.get();

            int next = (current >= Integer.MAX_VALUE ? 0 : current + 1);

            if (i.compareAndSet(current, next)) {

                return current;

            }

        }

    }



    public final int getAndDecrement() {

        for (;;) {

            int current = i.get();

            int next = (current <= 0 ? Integer.MAX_VALUE : current - 1);

            if (i.compareAndSet(current, next)) {

                return current;

            }

        }

    }



    public final int incrementAndGet() {

        for (;;) {

            int current = i.get();

            int next = (current >= Integer.MAX_VALUE ? 0 : current + 1);

            if (i.compareAndSet(current, next)) {

                return next;

            }

        }

    }



    public final int decrementAndGet() {

        for (;;) {

            int current = i.get();

            int next = (current <= 0 ? Integer.MAX_VALUE : current - 1);

            if (i.compareAndSet(current, next)) {

                return next;

            }

        }

    }



    public final int get() {

        return i.get();

    }



    public final void set(int newValue) {

        if (newValue < 0) {

            throw new IllegalArgumentException("new value " + newValue + " < 0");

        }

        i.set(newValue);

    }



    public final int getAndSet(int newValue) {

        if (newValue < 0) {

            throw new IllegalArgumentException("new value " + newValue + " < 0");

        }

        return i.getAndSet(newValue);

    }



    public final int getAndAdd(int delta) {

        if (delta < 0) {

            throw new IllegalArgumentException("delta " + delta + " < 0");

        }

        for (;;) {

            int current = i.get();

            int next = (current >= Integer.MAX_VALUE - delta + 1 ? delta - 1 : current + delta);

            if (i.compareAndSet(current, next)) {

                return current;

            }

        }

    }



    public final int addAndGet(int delta) {

        if (delta < 0) {

            throw new IllegalArgumentException("delta " + delta + " < 0");

        }

        for (;;) {

            int current = i.get();

            int next = (current >= Integer.MAX_VALUE - delta + 1 ? delta - 1 : current + delta);

            if (i.compareAndSet(current, next)) {

                return next;

            }

        }

    }



    public final boolean compareAndSet(int expect, int update) {

        if (update < 0) {

            throw new IllegalArgumentException("update value " + update + " < 0");

        }

        return i.compareAndSet(expect, update);

    }



    public final boolean weakCompareAndSet(int expect, int update) {

        if (update < 0) {

            throw new IllegalArgumentException("update value " + update + " < 0");

        }

        return i.weakCompareAndSet(expect, update);

    }



    public byte byteValue() {

        return i.byteValue();

    }



    public short shortValue() {

        return i.shortValue();

    }



    public int intValue() {

        return i.intValue();

    }



    public long longValue() {

        return i.longValue();

    }



    public float floatValue() {

        return i.floatValue();

    }



    public double doubleValue() {

        return i.doubleValue();

    }



    public String toString() {

        return i.toString();

    }



    @Override

    public int hashCode() {

        final int prime = 31;

        int result = 1;

        result = prime * result + ((i == null) ? 0 : i.hashCode());

        return result;

    }



    @Override

    public boolean equals(Object obj) {

        if (this == obj) return true;

        if (obj == null) return false;

        if (getClass() != obj.getClass()) return false;

        AtomicPositiveInteger other = (AtomicPositiveInteger) obj;

        if (i == null) {

            if (other.i != null) return false;

        } else if (!i.equals(other.i)) return false;

        return true;

    }



}