在java中使用key和vlue从两个不同的Map中获取Map键和值

Question

There are two Map, first one contains student id and name. second one contains student id and status of 'Pass' or 'Fail'. There is a method which takes two parameters of Map type and returns Map.

    //1st Map
    Map<Integer, String> map1 = new HashMap<>();
    map1.put(1, "x");
    map1.put(2, "y");
    map1.put(3, "z");
    map1.put(4, "a");
    map1.put(5, "b");`

and

    //2nd Map
    Map<Integer, String> map2 = new HashMap<>();
    map2.put(1, "fail");
    map2.put(2, "fail");
    map2.put(3, "fail");
    map2.put(4, "pass");
    map2.put(5, "pass");`

   //the method
public Map<Integer, String>findFaildStudent(Map<Integer, String>map1,Map<Integer, String>map2){
returns Map<Integer, String>;
 }

So, my question is how to find the record of failed students. I did try it myself but didn't succeed. Any help is appreciated.

What I tried so far

public Map<Integer, String>findFaildStudent(Map<Integer, String>map1,Map<Integer, String>map2){
    Integer key = null;
    String value = null;

    Iterator<Entry<Integer, String>> iterator = map1.entrySet().iterator();
    while(iterator.hasNext()){
        Entry<Integer, String> next = iterator.next();
        key = next.getKey();
    }

    Iterator<Entry<Integer, String>> iterator2 = map2.entrySet().iterator();
    while(iterator2.hasNext()){
        Entry<Integer, String> next = iterator2.next();
        value=next.getValue();
    }

    Map<Integer,String> hashMap = new HashMap<>();
    hashMap.put(key, value);

    return hashMap;

}

Answer 1

public Map<String, String> findFaildStudent(Map<Integer, String>map1,Map<Integer, String>map2){
    Map<String, String> failed = new HashMap<>();

    for (Map.Entry<Integer, String> k : map2.entrySet()) {
        if(k.getValue().equals("fail")){
            failed.put(map1.get(k.getKey()), map2.get(k.getValue()));
        }
    }
    return failed;
 }
//returns... ("x","failed"), ("y", "failed"), ("z", "failed")

So basically you just need to iterate through the 2nd map since it contain failed student, then you get the key and use that key to get the value of map1. You cannot concate the keys because the key is unique so if you want combine both map together it is better to create another map using map1(value) as key and map2(value) as value. Hope I understand your question but if you only want map2 of failed student then try below.

public Map<Integer, String> findFaildStudent(Map<Integer, String>map1,Map<Integer, String>map2){
Map<Integer, String> failed = new HashMap<>();

for (Map.Entry<Integer, String> k : map2.entrySet()) {
    if(k.getValue().equals("fail")){
        failed.put(k.getKey(), map1.get(k.getKey()));
    }
}
return failed;
//returns... (1,"x"), (2, "y"), (3, "z")

Answer 2

map1.entrySet().stream()
    .filter(entry -> "fail".equals(map2.get(entry.getKey())))
    .collect(Collectors.toMap(e -> e.getKey(), e -> e.getValue()));