循环遍历迭代器返回相同的值

Question

我有一个问题，我的循环没有中断并返回相同的值

public Map<String, String> getKeysByValue(Map<String, Map<String, Peple>> map, Collection<Peple> value) {
Map<String, String> stringStringMap = new HashMap<>();
int count = 0;
while (value.iterator().hasNext()) {
for (Map.Entry<String, Map<String, Peple>> entry : map.entrySet()) {
for (Map.Entry<String, Peple> entry1 : entry.getValue().entrySet()) {
String verified = value.iterator().next().gerVerfied();
if (verified.equals("true")) { 
stringStringMap.put(entry1.getKey(), value.iterator().next().getName());
}
}
}

这里的问题是，每个键(value.iterator((.next((.getName((在映射中放置的相同值总是返回相同的字符串

Answer 1

我认为以下将是解决您问题的正确方法：

public Map<String, String> getKeysByValue(Map<String, Map<String, Peple>> map, Collection<Peple> value) {
Map<String, String> stringStringMap = new HashMap<>();
int count = 0;
Iterator<People> peopleIterator = value.iterator();
while (peopleIterator.hasNext()) {
for (Map.Entry<String, Map<String, Peple>> entry : map.entrySet()) {
for (Map.Entry<String, Peple> entry1 : entry.getValue().entrySet()) {
People people = peopleIterator.next();
String verified = people.gerVerfied();
if (verified.equals("true")) {
stringStringMap.put(entry1.getKey(), people.getName());
}
}
}

您需要将迭代器存储在变量中。

考虑以下简单代码：

Collection<String> strings = new ArrayList<>();
strings.add("value1");
strings.add("value2");
strings.add("value3");
strings.add("value4");
while (strings.iterator.hasNext())
{
System.out.println(strings.iterator.next());
}

这将无限运行，并且只会打印 value1，但如果您按如下方式修改代码：

Collection<String> strings = new ArrayList<>();
strings.add("value1");
strings.add("value2");
strings.add("value3");
strings.add("value4");
Iterator<String> stringIterator = strings.iterator();
while (stringIterator.hasNext())
{
System.out.println(stringIterator.next());
}

它运行平稳。

您可以在此处了解有关迭代器的更多信息：https://www.geeksforgeeks.org/how-to-use-iterator-in-java/

ALso，我认为当您在第二次调用时调用迭代器两次而没有检查hasNext((，它可以抛出java.util.NoSuchElementException。

Answer 2

您在该迭代器上调用 next(( 两次。这会让它继续前进，并选取下一个人的名字，这可能无法验证。

我相信你只是想得到这个名字，如果它是一个经过验证的Peple？

while (value.iterator().hasNext()) {
for (Map.Entry<String, Map<String, Peple>> entry : map.entrySet()) {
for (Map.Entry<String, Peple> entry1 : entry.getValue().entrySet()) {
Peple nextPeple = value.iterator().next();
String verified = nextPeple.gerVerfied();
if (verified.equals("true")) { 
stringStringMap.put(entry1.getKey(), nextPeple.getName());
}
}
}
}

Answer 3

每次调用value.iterator()新的Iterator对象都是从头开始创建的，指向第一个元素。若要避免它，请将调用它的第一个结果存储到局部变量中。

Iterator<Peple> it = value.iterator();
while(it.hasNext()){
// your remaiing code
}

Answer 4

此代码适用于以下输入：

import java.util.*;
public class Test {
public static  void main(String[] ar){
Map<String, People> entry1 = new HashMap<String , People>();
People people1 = new People("true","name1");
People people2 = new People("false","name2");
People people3 = new People("true","name3");
entry1.put("user1", people1);
entry1.put("user2", people2);
entry1.put("user3", people3);
Map<String, People> entry2 = new HashMap<String , People>();
People people4 = new People("true","name1");
People people5 = new People("false","name2");
People people6 = new People("true","name3");
entry2.put("user1", people4);
entry2.put("user2", people5);
entry2.put("user3", people6);
Map<String, Map<String, People>> map2 = new HashMap<String, Map<String, 
People>>();
map2.put("set1",entry1);
map2.put("set2",entry2);
Collection<People> strings = new ArrayList<>();
strings.add(people1);
strings.add(people6);
strings.add(people5);
strings.add(people3);
strings.add(people2);
getKeysByValue(map2, strings);
}
public static Map<String, String> getKeysByValue(Map<String, Map<String, People>> map, Collection<People> value) {
Map<String, String> stringStringMap = new HashMap<>();
int count = 0;
Iterator<People> it = value.iterator();
while (it.hasNext()) {
People people = it.next();
for (Map.Entry<String, Map<String, People>> entry : map.entrySet()) {
for (Map.Entry<String, People> entry1 : entry.getValue().entrySet()) {
String verified = people.getVerified();
System.out.println(verified);
System.out.println("Key : "+entry1.getKey() +" Value : "+entry1.getValue().getVerified());
if (verified.equals(entry1.getValue().getVerified())) {
stringStringMap.put(entry1.getKey(), people.getName());
}
}
}
}
System.out.println(stringStringMap);
return stringStringMap;
}
}

人.java

public class People {
String verified;
public  People(String verified, String name){
this.verified = verified;
this.name = name;
}
public String getVerified() {
return verified;
}
public String getName() {
return name;
}
String name;

}

Answer 5

试试这个：

public Map<String, String> getKeysByValue(Map<String, Map<String, Peple>> map, Collection<Peple> value) {
Map<String, String> stringStringMap = new HashMap<>();
int count = 0;
Iterator<Peple> iterator = value.iterator();
while (iterator.hasNext()) {
Peple p = iterator.next();
for (Map.Entry<String, Map<String, Peple>> entry : map.entrySet()) {
for (Map.Entry<String, Peple> entry1 : entry.getValue().entrySet()) {
String verified = p.gerVerfied();
if (verified.equals("true")) { 
stringStringMap.put(entry1.getKey(), p.getName());
}
}
}
}
}