java list 映射实体 java数据映射

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fjfdh 2023-07-17 18:42:49

文章标签 java list 映射实体 java 向文件写数据结构 System java 迭代器 文章分类 Java 后端开发

Map映射数学定义：两个集合之间的元素对应关系

一个输入对应到一个输出

{1，张三}，{2.李四}，{Key,Value},键值对，K-V对

Java中MapHashtable(同步，慢，数据量小)

HashMap(不支持同步，快，数据量大)

Properties(同步，文件形式，数据量小)

HashtableK-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;
例程：
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class HashtableTest {
public static void main(String[] args) {
Hashtable ht =new Hashtable();
//ht.put(1, null); 编译不报错 运行报错//ht.put(null,1); 编译报错ht.put(1000, "aaa");
ht.put(2, "bbb");
ht.put(30000, "ccc");
System.out.println(ht.contains("aaa"));
System.out.println(ht.containsValue("aaa"));
System.out.println(ht.containsKey(30000));
System.out.println(ht.get(30000));
ht.put(30000, "ddd"); //更新覆盖cccSystem.out.println(ht.get(30000));
ht.remove(2);
System.out.println("size: " + ht.size());
ht.clear();
System.out.println("size: " + ht.size());
//测试遍历方法Hashtable ht2 =new Hashtable();
for(int i=0;i<100000;i++)
{
ht2.put(i, "aaa");
}
traverseByEntry(ht2);
traverseByKeySet(ht2);
traverseByKeyEnumeration(ht2);
}
public static void traverseByEntry(Hashtable ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry 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(Hashtable ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator iter = ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
// ��ȡvalue 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");
}
public static void traverseByKeyEnumeration(Hashtable ht)
{
long startTime = System.nanoTime();
System.out.println("============KeyEnumeration迭代器遍历==============");
Integer key;
String value;
Enumeration keys = ht.keys();//较老接口while(keys.hasMoreElements()) {
key = keys.nextElement();
// ��ȡvalue 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");
}
}
运行结果：
true
true
true
ccc
ddd
size: 2
size: 0
============Entry迭代器遍历==============
68430800纳秒
============KeySet迭代器遍历==============
57468700纳秒
============KeyEnumeration迭代器遍历==============
11452400纳秒
HashMapK-V对，K和V都允许为null
不同步，多线程不安全，变成同步：
Map m =Collections.synchronizedMap(new HashMap(···))；
无序的
主要方法;
clear;
containsValue;
containsKey;
get;
put;
remove;
size;
例程：
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class HashMapTest {
public static void main(String[] args) {
HashMap hm =new HashMap();
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cccSystem.out.println(hm.get(30000));
hm.remove(2);
System.out.println("size: " + hm.size());
hm.clear();
System.out.println("size: " + hm.size());
HashMap hm2 =new HashMap();
for(int i=0;i<100000;i++)
{
hm2.put(i, "aaa");
}
traverseByEntry(hm2);
traverseByKeySet(hm2);
}
public static void traverseByEntry(HashMap ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry entry = iter.next();
// ��ȡkey key = entry.getKey();
// ��ȡvalue 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(HashMap ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator iter = ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
// ��ȡvalue 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");
}
运行结果：
true
true
ccc
ddd
size: 4
size: 0
============Entry迭代器遍历==============
34918300纳秒
============KeySet迭代器遍历==============
19260000纳秒
LinkedHashMap基于双向链表的维持插入顺序的HashMap
例程：
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 hm =new LinkedHashMap();
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cccSystem.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> iter = hm.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry entry = iter.next();
// ��ȡkey key = entry.getKey();
// ��ȡvalue value = entry.getValue();
System.out.println("Key:" + key + ", Value:" + value);
}
System.out.println("遍历结束==================");
LinkedHashMap hm2 =new LinkedHashMap();
for(int i=0;i<100000;i++)
{
hm2.put(i, "aaa");
}
traverseByEntry(hm2);
traverseByKeySet(hm2);
}
public static void traverseByEntry(LinkedHashMap ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry entry = iter.next();
// ��ȡkey key = entry.getKey();
// ��ȡvalue 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 ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator iter = ht.keySet().iterator();
while(iter.hasNext()) {
key = iter.next();
// ��ȡvalue 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");
}
}
运行结果：
true
true
ccc
ddd
size: 4
遍历开始==================
Key:1, Value:null
Key:null, Value:abc
Key:1000, Value:aaa
Key:30000, Value:ddd
遍历结束==================
============Entry迭代器遍历==============
41830000纳秒
============KeySet迭代器遍历==============
12364800纳秒
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
例程：
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 hm =new TreeMap();
hm.put(1, null); //value可以为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cccSystem.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> iter = hm.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry 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 hm2 =new TreeMap();
for(int i=0;i<100000;i++)
{
hm2.put(i, "aaa");
}
traverseByEntry(hm2);
traverseByKeySet(hm2);
}
public static void traverseByEntry(TreeMap ht)
{
long startTime = System.nanoTime();
System.out.println("============Entry迭代器遍历==============");
Integer key;
String value;
Iterator> iter = ht.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry 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 ht)
{
long startTime = System.nanoTime();
System.out.println("============KeySet迭代器遍历==============");
Integer key;
String value;
Iterator 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");
}
}
输出结果
true
true
ccc
ddd
size: 4
遍历开始==================
Key:1, Value:null
Key:2, Value:bbb
Key:1000, Value:aaa
Key:30000, Value:ddd
遍历结束==================
============Entry迭代器遍历==============
38940500纳秒
============KeySet迭代器遍历==============
23699800纳秒
Properties继承于Hashtable
可以将K-V保存在文件中(唯一一个)
适用于数据量少的配置文件
继承自Hashtable的方法
contains/containsValue;
clear;
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
例程：
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类的常用操作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);
//从输入流读取属性列表(键和元素对) pps.load(in);
//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();
}

运行结果：

写入Test.properties================

加载Test.properties================

从Test.properties加载================

name is 12345

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