一：映射Map分类
二：Hashtable（同步，慢，数据量小）
–K-V对，K和V都不允许为null
–同步，多线程安全
–无序的
–适合小数据量
–主要方法：clear, contains/containsValue, containsKey, get,
put,remove, size
（一）基本使用方法
Hashtable<Integer,String> ht=new Hashtable<Integer,String>();
//ht.put(1, null); //编译不报错 运行时报错
//ht.put(null, "das");
ht.put(1000, "adad");
ht.put(200, "adsdad");
ht.put(1, "adadge");
//进行判断是否含有数据
System.out.println(ht.contains("adad"));
System.out.println(ht.containsValue("adad")); //contains和containsValue一样
System.out.println(ht.containsKey(1));
//进行数据获取
System.out.println(ht.get(1));
//进行更新
ht.put(1, "666"); //按照键，更新值
//进行移除
System.out.println(ht.containsKey(200));
ht.remove(200);
System.out.println(ht.containsKey(200));
//获取大小
System.out.println(ht.size());
true
true
true
adadge
true
false
2
（二）遍历方法
public static void traverseByEntry(Hashtable<Integer,String> ht){
long startTime = System.nanoTime();
System.out.println("=======Entry迭代器遍历=======");
Integer key;
String value;
Iterator<Entry<Integer,String>> iter=ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<Integer, String> ent= iter.next();
key = ent.getKey();
value=ent.getValue();
System.out.println(key+":"+value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
public static void traverseByKeySet(Hashtable<Integer,String> ht){
long startTime = System.nanoTime();
System.out.println("=======KeySet迭代器遍历=======");
Integer key;
String value;
Iterator<Integer> iter=ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
value=ht.get(key);
System.out.println(key+":"+value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
//Enumeration只在Hashtable中用到了，后面废弃不用
public static void traverseByKeyEnumeration(Hashtable<Integer,String> ht){
long startTime = System.nanoTime();
System.out.println("=======KeyEnumeration迭代器遍历=======");
Integer key;
String value;
Enumeration<Integer> keys=ht.keys(); //一次性获取所有的key值，
while(keys.hasMoreElements()) {
key = keys.nextElement();
// 获取value
value = ht.get(key);
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
（三）性能测试：数据量越大，差距越小
for(int i=0;i<10000;i++)
{
ht.put(i, "aaa");
}
//进行遍历
traverseByEntry(ht);
traverseByKeySet(ht);
traverseByKeyEnumeration(ht);
=======Entry迭代器遍历=======
13470233纳秒
=======KeySet迭代器遍历=======
8841551纳秒
=======KeyEnumeration迭代器遍历=======
4933705纳秒
三：HashMap（不支持同步，快，数据量大）
–K-V对，K和V都允许为nul
–不同步，多线程不安全
Map m = Collections.synchronizedMap(new HashMap(...));
–无序的
–主要方法：clear, containsValue, containsKey, get, put,remove, size
（一）基本使用方法一致
HashMap<Integer,String> hm =new HashMap<Integer,String>();
hm.put(1, null);
hm.put(null, "abc");
hm.put(1000, "aaa");
hm.put(2, "bbb");
hm.put(30000, "ccc");
System.out.println(hm.containsValue("aaa"));
System.out.println(hm.containsKey(30000));
System.out.println(hm.get(30000));
hm.put(30000, "ddd"); //更新覆盖ccc
System.out.println(hm.get(30000));
hm.remove(2);
System.out.println("size: " + hm.size());
hm.clear();
System.out.println("size: " + hm.size());
View Code（二）遍历方法除了没有Enumeration，其他一致
public static void traverseByEntry(HashMap<Integer,String> ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator<Entry<Integer, String>> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<Integer, String> entry = iter.next();
// 获取key
key = entry.getKey();
// 获取value
value = entry.getValue();
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
traverseByEntry
public static void traverseByKeySet(HashMap<Integer,String> ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator<Integer> iter = ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
// 获取value
value = ht.get(key);
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
traverseByKeySet
四：Properties (同步，文件形式，数据量小）
–继承于Hashtable
–可以将K-V对保存在文件
–适用于数据量少的配置文件
–继承自Hashtable的方法：clear, contains/containsValue, containsKey,
get, put,remove, size
–从文件加载的load方法， 写入到文件中的store方法
–获取属性 getProperty ，设置属性setProperty
（一）使用方法
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Enumeration;
import java.util.Properties;
//关于Properties类常用的操作
public class PropertiesTest {
//根据Key读取Value
public static String GetValueByKey(String filePath, String key) {
Properties pps = new Properties();
try {
InputStream in = new BufferedInputStream (new FileInputStream(filePath));
pps.load(in); //所有的K-V对都加载了
String value = pps.getProperty(key);
//System.out.println(key + " = " + value);
return value;
}catch (IOException e) {
e.printStackTrace();
return null;
}
}
//读取Properties的全部信息
public static void GetAllProperties(String filePath) throws IOException {
Properties pps = new Properties();
InputStream in = new BufferedInputStream(new FileInputStream(filePath));
pps.load(in); //所有的K-V对都加载了
Enumeration en = pps.propertyNames(); //得到配置文件的名字
while(en.hasMoreElements()) {
String strKey = (String) en.nextElement();
String strValue = pps.getProperty(strKey);
//System.out.println(strKey + "=" + strValue);
}
}
//写入Properties信息
public static void WriteProperties (String filePath, String pKey, String pValue) throws IOException {
File file = new File(filePath);
if(!file.exists())
{
file.createNewFile();
}
Properties pps = new Properties();
InputStream in = new FileInputStream(filePath);
//从输入流中读取属性列表（键和元素对）
pps.load(in); //先加载原来的文件键值对，在其基础上进行设置，再写入
//调用 Hashtable 的方法 put。使用 getProperty 方法提供并行性。
//强制要求为属性的键和值使用字符串。返回值是 Hashtable 调用 put 的结果。
OutputStream out = new FileOutputStream(filePath);
pps.setProperty(pKey, pValue);
//以适合使用 load 方法加载到 Properties 表中的格式，
//将此 Properties 表中的属性列表（键和元素对）写入输出流
pps.store(out, "Update " + pKey + " name");
out.close();
}
public static void main(String [] args) throws IOException{
System.out.println("写入Test.properties================");
WriteProperties("Test.properties","name", "12345");
System.out.println("加载Test.properties================");
GetAllProperties("Test.properties");
System.out.println("从Test.properties加载================");
String value = GetValueByKey("Test.properties", "name");
System.out.println("name is " + value);
}
}
五：LinkedHashMap和TreeMap
LinkedHashMap
–基于双向链表的维持插入顺序的HashMap
TreeMap
–基于红黑树的Map，可以根据key的自然排序或者compareTo方法进行排序输出
import java.util.LinkedHashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class LinkedHashMapTest {
public static void main(String[] args) {
LinkedHashMap<Integer,String> hm =new LinkedHashMap<Integer,String>();
hm.put(1, null);
hm.put(null, "abc");
hm.put(1000, "aaa");
hm.put(2, "bbb");
hm.put(30000, "ccc");
System.out.println(hm.containsValue("aaa"));
System.out.println(hm.containsKey(30000));
System.out.println(hm.get(30000));
hm.put(30000, "ddd"); //更新覆盖ccc
System.out.println(hm.get(30000));
hm.remove(2);
System.out.println("size: " + hm.size());
//hm.clear();
//System.out.println("size: " + hm.size());
System.out.println("遍历开始==================");
Integer key;
String value;
Iterator<Entry<Integer, String>> iter = hm.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<Integer, String> entry = iter.next();
// 获取key
key = entry.getKey();
// 获取value
value = entry.getValue();
System.out.println("Key:" + key + ", Value:" + value);
}
System.out.println("遍历结束==================");
LinkedHashMap<Integer,String> hm2 =new LinkedHashMap<Integer,String>();
for(int i=0;i<100000;i++)
{
hm2.put(i, "aaa");
}
traverseByEntry(hm2);
traverseByKeySet(hm2);
}
public static void traverseByEntry(LinkedHashMap<Integer,String> ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator<Entry<Integer, String>> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<Integer, String> entry = iter.next();
// 获取key
key = entry.getKey();
// 获取value
value = entry.getValue();
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
public static void traverseByKeySet(LinkedHashMap<Integer,String> ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator<Integer> iter = ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
// 获取value
value = ht.get(key);
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
}
LinkedHashMapTest
import java.util.TreeMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class TreeMapTest {
public static void main(String[] args) {
TreeMap<Integer,String> hm =new TreeMap<Integer,String>();
hm.put(1, null);
//hm.put(null, "abc"); 编译没错，运行报空指针异常
hm.put(1000, "aaa");
hm.put(2, "bbb");
hm.put(30000, "ccc");
System.out.println(hm.containsValue("aaa"));
System.out.println(hm.containsKey(30000));
System.out.println(hm.get(30000));
hm.put(30000, "ddd"); //更新覆盖ccc
System.out.println(hm.get(30000));
//hm.remove(2);
System.out.println("size: " + hm.size());
//hm.clear();
//System.out.println("size: " + hm.size());
System.out.println("遍历开始==================");
Integer key;
String value;
Iterator<Entry<Integer, String>> iter = hm.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<Integer, String> entry = iter.next();
// 获取key
key = entry.getKey();
// 获取value
value = entry.getValue();
System.out.println("Key:" + key + ", Value:" + value);
}
System.out.println("遍历结束==================");
TreeMap<Integer,String> hm2 =new TreeMap<Integer,String>();
for(int i=0;i<100000;i++)
{
hm2.put(i, "aaa");
}
traverseByEntry(hm2);
traverseByKeySet(hm2);
}
public static void traverseByEntry(TreeMap<Integer,String> ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator<Entry<Integer, String>> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<Integer, String> entry = iter.next();
// 获取key
key = entry.getKey();
// 获取value
value = entry.getValue();
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
public static void traverseByKeySet(TreeMap<Integer,String> ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator<Integer> iter = ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
// 获取value
value = ht.get(key);
//System.out.println("Key:" + key + ", Value:" + value);
}
long endTime = System.nanoTime();
long duration = endTime - startTime;
System.out.println(duration + "纳秒");
}
}
TreeMapTest
六：总结
–HashMap是最常用的映射结构
–如需要排序，考虑LinkedHashMap和TreeMap
–如需要将K-V存储为文件，可采用Properties类