Retrieving objects from HashMap in Java?

Question

I have a HashMap which holds studentIds as key and student objects as values,

HashMap<Integer, Student> hashMap = hashTables.buildHash(students);

public static HashMap<Integer, Student> buildHash(Student[] students) {
            HashMap<Integer, Student> hashMap = new HashMap<Integer, Student>();
            for (Student s : students) hashMap.put(s.getId(), s);
            return hashMap;
       }

the below code gets each KeyValue pair and s.getValue() returns a student object which is comprised of an id and an string name, how can i retrieve/print those values (student.int, student.name);

for(Map.Entry s : hashMap.entrySet())
    System.out.print(s.getKey()+" "+s.getValue());

Marko Topolnik · Accepted Answer · 2012-05-06 11:06:05Z

3

Just implement toString in Student and the code you posted will work as-is:

public class Student {
    ...
    public String toString() {
      return "ID = " + this.id + ", name = " + this.name;
    }
}

answered May 6, 2012 at 11:06

Marko Topolnik

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2 Comments

user1362208 Over a year ago

is there anyway that i could retrieve the int and string values of the object?

Marko Topolnik Over a year ago

See Michael Borgwardt's answer on that, he has it covered. The point is to use type parameters on the Map.Entry's declaration. Then you can freely write e.getValue().getId().

Michael Borgwardt · Accepted Answer · 2012-05-06 11:39:10Z

3

You just have to use the parameterized type for the entry:

for(Map.Entry<Integer, Student> s : hashMap.entrySet())
    System.out.print(s.getKey()+" "+s.getValue().getId()+" "+s.getValue().getName());

(note that it's impossible for a class to have a field named "int" because that's a language keyword).

edited May 6, 2012 at 11:39

answered May 6, 2012 at 11:05

Michael Borgwardt

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2 Comments

Michael Borgwardt Over a year ago

@Marko Topolnik: only because I was using the OP's syntax-violating infor about his class' structure

Marko Topolnik Over a year ago

Of course, I realized the humoristic aspect of it. Just that it's better to help than to mock :) Mind also that in the HashMap population code he uses a getter, so probably his id and name are private, as they should be.

user229044 · Accepted Answer · 2012-05-06 16:50:30Z

1

You can acheive this by..

for(Map.Entry<Integer, Student> s : hashMap.entrySet()){
    System.out.print(Long.valueof(s.getKey())+""+String.valueof(s.getValue().getName()));
}

edited May 6, 2012 at 16:50

user229044♦

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answered May 6, 2012 at 11:58

PVR

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