Returning the index number of an Arraylist in Java

Question

I would like my method public void showClassRoomDetails(String teacherName) to return the Arraylist index number using the teacherName.

Thanks

    import java.util.ArrayList;

public class School
{
private ArrayList<Classroom> classrooms;
private String classRoomName;
private String teacherName;

public School()
{
    classrooms =  new ArrayList<Classroom>();
}

public void addClassRoom(Classroom newClassRoom, String theClassRoomName)
{
    classrooms.add(newClassRoom);
    classRoomName = theClassRoomName;
}

public void addTeacherToClassRoom(int classroomId, String TeacherName)
{
    if (classroomId < classrooms.size() ) {
        classrooms.get(classroomId).setTeacherName(TeacherName);
    }
}

public void showClassRoomDetails(String teacherName)
{
    for (Classroom classroom : this.classrooms)
    {
        if (classroom.returnTeacherName().equals(teacherName))
        {
            System.out.println(classroom.returnClassRoomName());
            System.out.println(classroom.returnTeacherName());   
            break;
        }
    } 
}


}

Why did you downvote this? The "question" might be implicit, but clear enough, I guess? — Lukas Eder
– Lukas Eder, Commented Jan 5, 2011 at 14:56
a new user, but an extension of the following 'questions': stackoverflow.com/questions/4599283, stackoverflow.com/questions/4596544, stackoverflow.com/questions/4593232 — robert_x44
– robert_x44, Commented Jan 5, 2011 at 15:23
while many of us are willing to help on homework problems, you should be showing what you have done to try and solve a problem, and asking for specific help. We aren't here to write your homework one method at a time. — robert_x44
– robert_x44, Commented Jan 5, 2011 at 15:26

Lukas Eder · Accepted Answer · 2011-01-05 14:53:08Z

4

Use a regular loop, not the foreach loop:

public int showClassRoomDetails(String teacherName)
{
    for (int i = 0; i < this.classrooms.size(); i++)
    {
        Classroom classroom = classrooms.get(i);
        if (classroom.returnTeacherName().equals(teacherName))
        {
            return i;
        }
    } 

    // Return -1 when the teacher was not found
    return -1;
}

answered Jan 5, 2011 at 14:53

Lukas Eder

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Comments

DJClayworth · Accepted Answer · 2011-01-05 14:54:55Z

2

Either use a regular for loop (for (int i=0;i<classrooms.size();i++)) or use ArrayList.indexOf(classroom).

answered Jan 5, 2011 at 14:54

DJClayworth

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Comments

Buhake Sindi · Accepted Answer · 2011-01-05 14:55:12Z

0

Something like this?

for (int i = 0; i < classrooms.size(); i++) {
    Classroom classroom = classrooms.get(i);
    if (classroom.returnTeacherName().equals(teacherName)) {
        System.out.println("Index: " + i);
    }
}

Much more elegantly,

public int showClassRoomDetails(String teacherName) {
    for (int i = 0; i < classrooms.size(); i++) {
        Classroom classroom = classrooms.get(i);
        if (classroom.returnTeacherName().equals(teacherName)) {
            return i;
        }
    }

    return -1;
}

Alternatively, keep a counter that gets incremented for each not true condition (on your if statement).

answered Jan 5, 2011 at 14:55

Buhake Sindi

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Comments

卢声远 Shengyuan Lu · Accepted Answer · 2011-01-05 15:02:07Z

0

//Return set containing multiple matched indexes
public Set<Integer> showClassRoomDetails(String teacherName){
     Set<Integer> result = new HashSet<Integer>();
     int i=0;
     for (Classroom classroom : this.classrooms){
         if (classroom.returnTeacherName().equals(teacherName))
           result.add(i);
         i++;
     } 
   return result;
 }

edited Jan 5, 2011 at 15:02

answered Jan 5, 2011 at 14:56

卢声远 Shengyuan Lu

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