java HashMap的使用-优快云博客

本文介绍了在Java中遍历Map的不同方法，包括使用迭代器、foreach循环等，并提供了具体示例代码。此外还展示了如何使用HashMap存储学生成绩并计算平均分。

Java中怎样遍历Map的所有的元素：

JDK1.4中

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Map map = new HashMap();

Iterator it = map.entrySet().iterator();

while (it.hasNext()) {

Map.Entry entry = (Map.Entry) it.next();

Object key = entry.getKey();

Object value = entry.getValue();

}

Map map = new HashMap();

Iterator it = map.entrySet().iterator();

while (it.hasNext()) {

Map.Entry entry = (Map.Entry) it.next();

Object key = entry.getKey();

Object value = entry.getValue();

}JDK1.5中,应用新特性For-Each循环

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Map m = new HashMap();

for(Object o : map.keySet()){

map.get(o);

}

Map m = new HashMap();

for(Object o : map.keySet()){

map.get(o);

}返回的 set 中的每个元素都是一个 Map.Entry 类型。

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private Hashtable<String, String> emails = new Hashtable<String, String>();

private Hashtable<String, String> emails = new Hashtable<String, String>(); 另外我们可以先把hashMap 转为集合Collection，再迭代输出，不过得到的对象

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//方法一: 用entrySet()

Iterator it = emails.entrySet().iterator();

while(it.hasNext()){

Map.Entry m=(Map.Entry)it.next();

logger.info("email-" + m.getKey() + ":" + m.getValue());

}

// 方法二：jdk1.5支持，用entrySet()和For-Each循环()

for (Map.Entry<String, String> m : emails.entrySet()) {

logger.info("email-" + m.getKey() + ":" + m.getValue());

}

// 方法三：用keySet()

Iterator it = emails.keySet().iterator();

while (it.hasNext()){

String key;

key=(String)it.next();

logger.info("email-" + key + ":" + emails.get(key));

}

// 方法五：jdk1.5支持，用keySEt()和For-Each循环

for(Object m: emails.keySet()){

logger.info("email-" + m+ ":" + emails.get(m));

}

//方法一: 用entrySet()

Iterator it = emails.entrySet().iterator();

while(it.hasNext()){

Map.Entry m=(Map.Entry)it.next();

logger.info("email-" + m.getKey() + ":" + m.getValue());

}

// 方法二：jdk1.5支持，用entrySet()和For-Each循环()

for (Map.Entry<String, String> m : emails.entrySet()) {

logger.info("email-" + m.getKey() + ":" + m.getValue());

}

// 方法三：用keySet()

Iterator it = emails.keySet().iterator();

while (it.hasNext()){

String key;

key=(String)it.next();

logger.info("email-" + key + ":" + emails.get(key));

}

// 方法五：jdk1.5支持，用keySEt()和For-Each循环

for(Object m: emails.keySet()){

logger.info("email-" + m+ ":" + emails.get(m));

}

HashMap的插入

用HashMap类完成:

考号组成:学号+课程编号+系统日期例如:s19303C2007723
分数:在0-10之间
考号作为键,分数作为值.
要求分别录入5名学员信息,统计5名学员中参加JAVA考试的平均成绩.

集合类这学的不是很好~尤其是HashMap类.希望大家多多帮忙~要详细过程

import java.util.HashMap;
import java.util.Iterator;

public class Test {
public static void main(String args[]) {
HashMap<String, Integer> map = new HashMap<String, Integer>();
map.put("s19303C2007723 ", 8);
map.put("s19303C2007724 ", 6);
map.put("s19303C2007725 ", 4);
map.put("s19303C2007726 ", 8);
map.put("s19303C2007727 ", 3);

int sum = 0;

for (Iterator<String> i = map.keySet().iterator(); i.hasNext();) {
String key = i.next();
int value = map.get(key);
sum += value;
}

System.out.println(sum / (double) 5);
}
}