Map的常见之类
HashMap， HashTable， TreeMap， WeakHashMap， IdentityHashMap
最常用的HashMap的使用方法:
import java.util.*;
public class HashMapDemo {
public static void main(String args[]) {
HashMap<String,String> hm = new HashMap<String,String>();
hm.put("0","00");
hm.put("1","11");
hm.put("2","22");
hm.put("3","33");
System.out.println(hm.keySet());
System.out.println(hm.values());
System.out.println(hm.get("1"));
System.out.println(hm.size());
//Map.Entry
Set<Map.Entry<String,String>> es = hm.entrySet();
Iterator<Map.Entry<String, String>> it = es.iterator();
while(it.hasNext()) {
Map.Entry<String,String> me = it.next();
System.out.println(me.getKey()+"_"+me.getValue());
}
//foreach Map.Entry
for(Map.Entry<String,String> me:hm.entrySet()){
System.out.println(me.getKey()+"_"+me.getValue());
}
Set<String> hs = hm.keySet();
Iterator it0 = hs.iterator();
while(it0.hasNext()) {
String key = (String)it0.next();
System.out.println( key +"_" +hm.get(key));
}
}
}
HashMap
HashMap的键值重复
HashMap判断key重复是根据key的equals()和hashCode() 判断，如果key的equals是相等和hasCode是相等的话，那就认为元素是重复的， 不往map中存放：
HashMap类和HashSet类判断元素是否重复方式是一样的
import java.util.*;
class Person{
public String name = "";
public Person(String name){
this.name = name;
}
public boolean equals( Object p) {
if( this == p) {
return true;
};
if( p instanceof Person ) {
Person pp = (Person)p;
if(this.name == pp.name){
return true;
}else{
return false;
}
}else{
return false;
}
}
public int hashCode(){
return this.name.hashCode();
}
public String toString(){
return this.name;
}
}
public class HashMapRepeatDemo {
public static void main(String args[]) {
Map<Person,String> hm = new HashMap<Person,String>();
hm.put(new Person("nono"), "1");
hm.put(new Person("11"), "2");
hm.put(new Person("nono"), "1");
hm.put(new Person("nono"), "1");
System.out.println(hm);
}
}
IdentityHashMap
IdentityHashMap允许往HashMap中存放key值重复的对象。
import java.util.*;
class Person{
public String name = "";
public Person(String name){
this.name = name;
}
public boolean equals( Object p) {
if( this == p) {
return true;
};
if( p instanceof Person ) {
Person pp = (Person)p;
if(this.name == pp.name){
return true;
}else{
return false;
}
}else{
return false;
}
}
public int hashCode(){
return this.name.hashCode();
}
public String toString(){
return this.name;
}
}
public class IdentityHashMapDemo{
public static void main(String args[]) {
Map<Person,String> hm = new IdentityHashMap<Person,String>();
hm.put(new Person("nono"), "1");
hm.put(new Person("11"), "2");
hm.put(new Person("nono"), "1");
hm.put(new Person("nono"), "1");
for(Map.Entry<Person,String> me:hm.entrySet()) {
System.out.print("instanceof Person : ");
System.out.println(me.getKey() instanceof Person);
System.out.print("key is : ");
System.out.println(me.getKey());
System.out.print("value is : ");
System.out.println(me.getValue());
}
System.out.println(hm);
}
}
SortedMap
SortedMap是TreeMap的抽象实现， 要使用SortedMap，必须要new TreeMap();
import java.util.*;
public class SortedHashMapDemo {
public static void main(String args[]) {
SortedMap<String, String> sm = new TreeMap<String, String>();
sm.put("aa","aa");
sm.put("bb","bb");
sm.put("cc","cc");
sm.put("dd","dd");
System.out.println(sm);
System.out.println(sm.firstKey());
System.out.println(sm.lastKey());
System.out.println(sm.subMap("aa","dd"));
System.out.println(sm.headMap("dd"));
System.out.println(sm.tailMap("aa"));
}
}
TreeMap
import java.util.*;
public class TreeMapDemo {
public static void main(String args[]) {
TreeMap<String,String> tm = new TreeMap<String,String>();
tm.put("a","a");
System.out.println(tm);
}
}
Collections
Collections这个工具类也可以作为Set或者List的辅助方法， 只是平常可能用的少， 利用Collection可以实现addAll的功能， 参数是可变的;
import java.util.*;
public class CollectionsDemo {
public static void main(String args[]) {
//Collections.emptyList();
List<String> allList = new ArrayList<String>();
Set<String> allSet = Collections.emptySet();
//allList.add("hello"); <<== Wrong
//allList.add("world"); <<== Wrong
String[] strArray="Sweet0,Sour0".split(",");
Collections.addAll(allList, strArray);
Collections.addAll(allList, ":");
System.out.println(allList);
}
}
Stack类栈的操作
Stack的search是从栈底一直往上堆彻的， 所以使用search时候输出的index和ArrayList是相反的
import java.util.*;
public class StackDemo {
public static void main(String args[]) {
Stack<String> sk = new Stack<String>();
//push
sk.push("a");
sk.push("b");
sk.push("C");
sk.push("d");
System.out.println(sk);
//peek
System.out.println(sk.peek());
//pop
System.out.println(sk.pop());
System.out.println(sk);
//search
System.out.println(sk.search("a")); //这个居然输出3
System.out.println(sk.search("b")); //这个输出2
System.out.println(sk.search("C")); //这个输出1
//size
System.out.println(sk.size());
}
}
properties类
这个要配合xml进行存储， 一般用来保存配置的
import java.util.*;
import java.io.*;
public class PropertyDemo {
public static void main(String args[]) {
Properties pro = new Properties();
pro.setProperty("xx","xx");
pro.setProperty("yy","yy");
pro.setProperty("zz","zz");
System.out.println(pro.getProperty("xx"));
File file = new File("H:\\work\\java\\demo\\web\\xx.properties");
try{
pro.store(new FileOutputStream(file), "Info");
}catch(Exception e){
e.printStackTrace();
}
}
}
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