59-知識筆記(java-集合詳解03)
阿新 • • 發佈:2020-12-21
技術標籤:知識點積累
Map介面:雙列集合 key—value對應
Map介面方法:
key是不能重複的!!!!
Map遍歷(Key檢視遍歷):
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
public class Case02 {
public static void main(String[] args) {
HashMap<Object, Object> map = new HashMap<>();
map.put (1, "jack");
map.put(2, "rose");
map.put(3, "lucy");
map.put(4, "hello");
map.put(5, "lili");
Set<Object> keySet = map.keySet();
Iterator<Object> iterator = keySet.iterator();
while ( iterator.hasNext()){
Object key = iterator.next();
Object value = map.get(key);
System.out.println(key + ":" + value);
}
}
}
Map遍歷(values檢視遍歷):
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
public class Case03 {
public static void main(String[] args) {
HashMap<Object, Object> map = new HashMap<>();
map.put(1, "jack");
map.put(2, "rose");
map.put(3, "lucy");
map.put(4, "hello");
map.put(5, "lili");
Collection<Object> values = map.values();
Iterator<Object> iterator = values.iterator();
while (iterator.hasNext()){
System.out.println(iterator.next());
}
}
}
LinkedHashMap用法:用來維護寫讀順序
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
public class Case04 {
public static void main(String[] args) {
LinkedHashMap<Object, Object> map = new LinkedHashMap<>();
map.put(3,"jack");
map.put(2,"sss");
map.put(4, "tttt");
Set<Object> KeySet = map.keySet();
Iterator<Object> it = KeySet.iterator();
while (it.hasNext()){
Object key = it.next();
Object value = map.get(key);
System.out.println(key + ":" + value);
}
}
}
Map介面還有一個實現類Hashtable, 它和HashMap十分相似,區別在於Hashtable是執行緒安全的。Hashtable存取元素時速度很慢,目前基本上被HashMap類所取代。
但Hashtable類有一個子類Properties在實際應用中非常重要。
Properties主要用來儲存字串型別的鍵和值,在實際開發中,經常使用Properties集合來存取應用的配置項。比如以下的字串格式:
Backgroup-color=red
Font-size=14px
import java.util.Enumeration;
import java.util.Properties;
public class Case05 {
public static void main(String[] args) {
Properties p = new Properties();
p.setProperty("back","red");
p.setProperty("font","14px");
p.setProperty("language","chinese");
Enumeration<?> name = p.propertyNames();
while (name.hasMoreElements()){
String key = (String) name.nextElement();
String value = p.getProperty(key);
System.out.println(key + ":" + value);
}
}
}