[java] How to call a method in another class in Java?

Currently I have two classes. a classroom class and a School class. I would like to write a method in the School class to call public void setTeacherName(String newTeacherName) from the classroom class.

classroom.java

public class classroom {
    private String classRoomName;
    private String teacherName;

    public void setClassRoomName(String newClassRoomName) {
        classRoomName = newClassRoomName;

    }

    public String returnClassRoomName() {
        return classRoomName;
    }

    public void setTeacherName(String newTeacherName) {
        teacherName = newTeacherName;

    }

    public String returnTeacherName() {
        return teacherName;
    }
}

School.java

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;
    }

    // how to write a method to add a teacher to the classroom by using the
    // classroom parameter
    // and the teachers name
}  

Instead of using this in your current class setClassRoomName("aClassName"); you have to use classroom.setClassRoomName("aClassName");

You have to add the class' and at a point like

yourClassNameWhereTheMethodIs.theMethodsName();

I know it's a really late answer but if someone starts learning Java and randomly sees this post he knows what to do.

class A{
  public void methodA(){
    new B().methodB();
    //or
    B.methodB1();
  }
}

class B{
  //instance method
  public void methodB(){
  }
  //static method
  public static  void methodB1(){
  }
}

Try this :

public void addTeacherToClassRoom(classroom myClassRoom, String TeacherName)
{
    myClassRoom.setTeacherName(TeacherName);
}

You should capitalize names of your classes. After doing that do this in your school class,

Classroom cls = new Classroom();
cls.setTeacherName(newTeacherName);

Also I'd recommend you use some kind of IDE such as eclipse, which can help you with your code for instance generate getters and setters for you. Ex: right click Source -> Generate getters and setters

in School,

public void addTeacherName(classroom classroom, String teacherName) {
    classroom.setTeacherName(teacherName);
}

BTW, use Pascal Case for class names. Also, I would suggest a Map<String, classroom> to map a classroom name to a classroom.

Then, if you use my suggestion, this would work

public void addTeacherName(String className, String teacherName) {
    classrooms.get(className).setTeacherName(teacherName);
}