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
}