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HashMapTest.java
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74 lines (63 loc) · 2.22 KB
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package CollectionTest;
import java.util.Dictionary;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
/*
* public class HashMap<K,V> extends AbstractMap<K,V>
implements Map<K,V>, Cloneable, Serializable {
AbstractMap 实现了Map接口，HashMap继承自AbstractMap,AbstractMap实现了Map的大部分方法
线程不安全
http://www.cnblogs.com/skywang12345/p/3310835.html //详情请看这篇博文
* */
/*
* Map允许键、值为null;
* */
/* 问题1：
final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
int s = m.size();
//计算容量
if (s > 0) {
if (table == null) { // pre-size
float ft = ((float)s / loadFactor) + 1.0F;
int t = ((ft < (float)MAXIMUM_CAPACITY) ?
(int)ft : MAXIMUM_CAPACITY);
if (t > threshold)
threshold = tableSizeFor(t);
}
else if (s > threshold)
resize();
//循环为其赋值
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
K key = e.getKey();
V value = e.getValue();
putVal(hash(key), key, value, false, evict);
}
// 继续查看putVal()函数可以发现 Map的拷贝只是拷贝了Map的第一个元素，而不是一整个Entry链
}
}
* */
/*HashTable 类声明
* 1.public class Hashtable<K,V>
extends Dictionary<K,V>
implements Map<K,V>, Cloneable, java.io.Serializable {
*实现了Map、Dictionary接口，线程安全，与HashMap一样都是散列表，使用拉链法解决Hash冲突
* 2.
* public V setValue(V value) {
if (value == null)
throw new NullPointerException();
V oldValue = this.value;
this.value = value;
return oldValue;
}
HashTable不允许键值出现Null，出现则抛出 NullPointerException();
* */
public class HashMapTest {
public static void main(String[] args) {
//1.
Map Test = new HashMap<Integer, String>();
// Test.put(null, "s");
// Test.put(1, null);
Dictionary table=new Hashtable<String,Integer>();
}
}