C06 原型模式 Mybatis + JDK源码解析

最新推荐文章于 2021-06-13 00:23:27 发布

原创最新推荐文章于 2021-06-13 00:23:27 发布 · 179 阅读

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本文探讨了原型模式在Java中的实现方式，通过分析org.apache.ibatis.cache.CacheKey和java.util.HashMap两个类的具体代码，展示了如何利用Cloneable接口来实现对象的深拷贝，从而避免在创建新对象时重复构造过程，提高效率。

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太多了，只要实现了Cloneable接口的类都使用了原型模式；

org.apache.ibatis.cache.CacheKey

public class CacheKey implements Cloneable, Serializable {
    private static final long serialVersionUID = 1146682552656046210L;
    public static final CacheKey NULL_CACHE_KEY = new NullCacheKey();
    private static final int DEFAULT_MULTIPLYER = 37;
    private static final int DEFAULT_HASHCODE = 17;
    private int multiplier;
    private int hashcode;
    private long checksum;
    private int count;
    private List<Object> updateList;

    public CacheKey clone() throws CloneNotSupportedException {
        CacheKey clonedCacheKey = (CacheKey)super.clone();
        clonedCacheKey.updateList = new ArrayList(this.updateList);
        return clonedCacheKey;
    }

}

java.util.HashMap

public class HashMap<K,V> extends AbstractMap<K,V>
    implements Map<K,V>, Cloneable, Serializable {

    /**
     * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
     * values themselves are not cloned.
     *
     * @return a shallow copy of this map
     */
    @SuppressWarnings("unchecked")
    @Override
    public Object clone() {
        HashMap<K,V> result;
        try {
            result = (HashMap<K,V>)super.clone();
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError(e);
        }
        result.reinitialize();
        result.putMapEntries(this, false);
        return result;
    }

}