Java Quiz 29: Working with objects and references

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Java Quiz 29: Working with objects and references

Level: Normal

What is the output of the following code?

public class Test
{
  static Student st = new Student("Emma");
  
  public static void main(String[] args)
  {
    Student st = new Student("Vera");
    Test ts = new Test();
    ts.st = st;
    ts.st.change(st);
    System.out.print(st.name + ", ");
    System.out.print(new Test().st.name);
  }
}
class Student
{
  String name;
  
  public Student(String name)
  {
    this.name = name;
  }
  public void change(Student student)
  {
    student = new Student("David");
  }
}
Author: Sar Maroof

Select the correct answer.
a. This program writes “David, Emma” to the standard output.
b. This program writes “David, Vera” to the standard output.
c. This program writes “Vera, Vera” to the standard output.
d. This program writes “Vera, Emma” to the standard output.
e. Runtime error.
f. Compilation error.

Answer explanation

  1. The statement Student st = new Student(“Vera”); assigns the name Vera to the name of the student object st.
  2. The statement ts.st = st; assigns the object st to the reference ts.st.
  3. Remember that the the object ts.st is static, which belongs to the class.
  4. The statement ts.st.change(st); doesn’t change the refernce st, because the value of the of the object st is passed to the method change not its reference.
  5. So, the statements System.out.print(st.name + “, “); and System.out.print(new Test().st.name); write Vera, Vera to the standard output.

The correct answer is: c.

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Sar Maroof is graduated from HBO Amsterdam "higher professional education". He is a professional computer programming teacher, gives master classes and publishes technical articles. His experience with developing software started from 2001 and he has worked as a software developer for several big as well as small companies and later as a freelancer. He is the author of Java quizmaster and Build a Java application in 7 days.

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