对于Map来说,遍历的方式都是一样的,大概都是有四种形式 - 直接遍历
- 返回keySet()
- 返回Values()
- 返回entrySet()
import java.util.*;
public class HashMapDemo {
public static void main(String[] args) {
Map hm = new HashMap<>();
hm.put("姓名", "Jack");
hm.put("age", 18);
hm.put("身高", '?');
hm.put("身高", 178);
// 键和值都允许为 null
hm.put(null, null);
// 直接输出该对象
System.out.println("直接打印");
System.out.println(hm);
// 第一种遍历方式 : jdk1.8 新特性
map.forEach((k, v) -> System.out.println(k+"..."+v));
// 第二种遍历方式 : 通过返回键集
System.out.println("keySet()");
Set keySet = hm.keySet();
Iterator iter = keySet.iterator();
while (iter.hasNext()) {
Object next = iter.next();
System.out.println(next + "," + hm.get(next));
}
/*
首先返回的都是集合类型,除了可以使用iterator进行遍历外,还可以使用增强for循环也是非常方便的.
其实增强for循环就是上面形式的简写.本质也是上面的形式.
*/
// 增强for循环
System.out.println("增强for循环");
for (Object s :
keySet) {
System.out.println(s + "," + hm.get(s));
}
// 第三种遍历方式 : 通过返回值集
System.out.println("value()");
Collection values = hm.values();
Iterator iter1 = values.iterator();
while (iter1.hasNext()) {
System.out.println(iter1.next());
}
// 第四种遍历方式 : 通过返回key-value集
System.out.println("entrySet()集");
Iterator iter2 = hm.entrySet().iterator();
while (iter2.hasNext()) {
System.out.println(iter2.next());
}
/*
第四种方式的细化,将返回的key-value集分别取出
*/
while (iter2.hasNext()) {
Map.Entry next = (Map.Entry) iter2.next();
System.out.println(next.getKey() + " . " + next.getValue());
}
/*
第四种方式细化的简化形式.
*/
Set<Map.Entry> entrySet = hm.entrySet();
for (Map.Entry e : entrySet) {
System.out.println(e.getKey() + " , " + e.getValue());
}
}
}
import java.io.PrintStream;
import java.util.*;
public class HashMapDemo
{
public HashMapDemo()
{
}
public static void main(String args[])
{
Map hm = new HashMap();
hm.put("姓名", "Jack");
hm.put("age", Integer.valueOf(18));
hm.put("身高", Character.valueOf('?'));
hm.put("身高", Integer.valueOf(178));
hm.put(null, null);
System.out.println("直接打印");
System.out.println(hm);
System.out.println("keySet()");
Set keySet = hm.keySet();
Object next;
for (Iterator iter = keySet.iterator(); iter.hasNext();
System.out.println((new StringBuilder()).append(next).append(",").append(hm.get(next)).toString()))
next = iter.next();
System.out.println("增强for循环");
Object s;
for (Iterator iterator = keySet.iterator(); iterator.hasNext();
System.out.println((new StringBuilder()).append(s).append(",").append(hm.get(s)).toString()))
s = iterator.next();
System.out.println("value()");
Collection values = hm.values();
for (Iterator iter1 = values.iterator(); iter1.hasNext(); System.out.println(iter1.next()));
System.out.println("entrySet()集");
Iterator iter2;
for (iter2 = hm.entrySet().iterator(); iter2.hasNext(); System.out.println(iter2.next()));
java.util.Map.Entry next;
for (; iter2.hasNext();
System.out.println((new StringBuilder()).append(next.getKey()).append(" . ").append(next.getValue()).toString()))
next = (java.util.Map.Entry)iter2.next();
Set entrySet = hm.entrySet();
java.util.Map.Entry e;
for (Iterator iterator1 = entrySet.iterator(); iterator1.hasNext();
System.out.println((new StringBuilder()).append(e.getKey()).append(" , ").append(e.getValue()).toString()))
e = (java.util.Map.Entry)iterator1.next();
}
}