详解Java集合类之HashTable,Properties篇

Hashtable hashtable = new Hashtable();
hashtable.put("john",100);
hashtable.put("tom",250);
hashtable.put("tom",1314);
System.out.println(hashtable);

if (value == null) {
    throw new NullPointerException();
}

addEntry(hash, key, value, index);

private void addEntry(int hash, K key, V value, int index) {
    Entry<?,?> tab[] = table;
    if (count >= threshold) {
        // Rehash the table if the threshold is exceeded
        rehash();

        tab = table;
        hash = key.hashCode();
        index = (hash & 0x7FFFFFFF) % tab.length;
    }

    // Creates the new entry.
    @SuppressWarnings("unchecked")
    Entry<K,V> e = (Entry<K,V>) tab[index];
    tab[index] = new Entry<>(hash, key, value, e);
    count++;
    modCount++;
}

if (count >= threshold) {
    // Rehash the table if the threshold is exceeded
    rehash();
    tab = table;
    hash = key.hashCode();
    index = (hash & 0x7FFFFFFF) % tab.length;
}

protected void rehash() {
    int oldCapacity = table.length;
    Entry<?,?>[] oldMap = table;

    // overflow-conscious code
    int newCapacity = (oldCapacity << 1) + 1;
    if (newCapacity - MAX_ARRAY_SIZE > 0) {
        if (oldCapacity == MAX_ARRAY_SIZE)
            // Keep running with MAX_ARRAY_SIZE buckets
            return;
        newCapacity = MAX_ARRAY_SIZE;
    }
    Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];

    modCount++;
    threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
    table = newMap;

    for (int i = oldCapacity ; i-- > 0 ;) {
        for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
            Entry<K,V> e = old;
            old = old.next;

            int index = (e.hash & 0x7FFFFFFF) % newCapacity;
            e.next = (Entry<K,V>)newMap[index];
            newMap[index] = e;
        }
    }
}

int oldCapacity = table.length;

int newCapacity = (oldCapacity << 1) + 1;

Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];

import java.util.Properties;

/**
 * Properties演示
 */
public class PropertiesText {
    @SuppressWarnings({"all"})
    public static void main(String[] args) {
        Properties properties = new Properties();
        // 增加
        properties.put("john",521);
        properties.put("tom",1314);
        properties.put("tom",100);
        System.out.println(properties);
        // 通过key获取值
        System.out.println(properties.get("tom"));
        // 删除
        properties.remove("tom");
        System.out.println(properties);
    }
}