Poll 08-19: Reference Variables and Unix

Unix File Hierarchy

Note

This question tests the students’ ability to understand the Unix File Hierarchy using sample output from the tree command. The exercise is very similar to the book question in section 2.7 - Additional Practice.

Question 1

Suppose that you are working directly inside of your home directory on Odin, execute the tree command, and observe the output below:

output from the Unix ``tree`` command showing the directory structure.

If /home/users/user is the absolute path to your present working directory (also your home directory), then which of the commands shown below would move you directly into the 1302 directory? Select all that apply.

Choices (Students should refer to what is shown on eLC)

  1. cd /home/users/user/exercise1/school/1302

  2. cd exercise1/school/1302

  3. cd 1302

  4. cd ~/1302

  5. cd ~/exercise1/school/1302

  6. cd /exercise1/school/1302

Solution

a, b, e

Memory Map: Person Class

Note

This question tests the students’ ability to understand code that declares multiple reference variables and objects. It also tests whether or not they understand that two variables can reference the same object.

The exercise is very similar to the book question in section 1.3 - Reference Type Examples.

Person Class

Consider the code for a Person class below, which is used throughout this question.

 1public class Person {
 2
 3   private String name;
 4   private int age;
 5
 6   public Person(String name, int age) {
 7      this.name = name;
 8      this.age = age;
 9   } // Person
10
11   public int getAge() {
12       return this.age;
13   } // getAge
14
15   public void setAge(int age) {
16      this.age = age;
17   } // setAge
18
19} // Person
Question 2

Draw a memory map diagram depicting the state of the variables after the first half of the code below executes. Once your memory map is complete, select the correct option below that matches the output from the last three lines of code (marked “second half”).

// first half
Person susan = new Person("Susan", 23);
Person bill = new Person("Bill", 22);
Person p = bill;
p.setAge(43);

// second half
System.out.println(susan.getAge());
System.out.println(bill.getAge());
System.out.println(p.getAge());
Choices (Students should refer to what is shown on eLC)
  1. 23
22
43

  2. 43
43
43

  3. 23
43
43

  4. 23
23
43

  5. 23
23
23

  6. This code will not compile, so there will be no output.

Solution
Solution

c