我把一个字符串数组的元素放在一个映射表中,其中字符串数组的元素是键,单词频率是值,例如:
String[] args = {"if","it","is","to","be","it","is","up","me","to","delegate"};
那么这个映射将会包含类似于 [ if:1, it:2 .... ]
的条目。
Set<String> keys = m.keySet();
System.out.println("keyset of the map : "+keys);
打印所有键:"if","it","is","to","be","it","is","up","me","to","delegate"
Set<Map.Entry<String, Integer>> entrySet = m.entrySet();
Iterator<Map.Entry<String, Integer>> i = entrySet.iterator();
while(i.hasNext()){
Map.Entry<String, Integer> element = i.next();
System.out.println("Key: "+element.getKey()+" ,value: "+element.getValue());
}
打印所有键值对:
使用entry set打印所有值:
Key: if ,value: 1
Key: it ,value: 2
Key: is ,value: 2
Key: to ,value: 2
Key: be ,value: 1
Key: up ,value: 1
Key: me ,value: 1
Key: delegate ,value: 1
但是下面的代码块应该打印出与上述相同的输出,但实际上并没有:
Iterator<String> itr2 = keys.iterator();
while(itr2.hasNext()){
//System.out.println(itr1.next()+" ");
//System.out.println(m.get(itr1.next())+" ");
System.out.println("Key: "+itr2.next()+" ,value: "+m.get(itr2.next()));
}
它会输出:
Key: if ,value: 2
Key: is ,value: 2
Key: be ,value: 1
Key: me ,value: 1
但是,如果我们取消while循环中的第1行注释,即:
System.out.println(itr1.next()+" ");
注释掉这行代码
System.out.println("Key: "+itr2.next()+" ,value: "+m.get(itr2.next()));
然后我们获取所有键:{"if","it","is","to","be","it","is","up","me","to","delegate"}
如果我们在使用m.get()
时与itr2.next()
一起使用,那么迭代器将没有几个键!