Section 1

Agenda
Getting started
Preliminary Java questions
Debugging exercise
Other Java exercises

Agenda

Finding section 0 solutions
Using Ed Discussion
Accessing our Common Errors page for help fixing syntax errors
Java exercises

Getting started

Create a folder named section1 for your work on these exercises. You can find instructions for doing so here.
In VS Code, select the File->Open Folder or File->Open menu option, and use the resulting dialog box to find and open your section1 folder. The name of the folder should appear in the Explorer pane on the left-hand side of the VS Code window.

Important: In general, you should not use File->Open File to open a specific file in VS Code. Rather, you should create a folder for the files that belong to a given assignment or section, and you should use File->Open Folder or File->Open to open the folder.

Preliminary Java questions

In Java, what is an identifier? ¹
Indicate whether the following names are valid Java identifiers. ²
1. SECRET_NUMBER
2. average?num
3. 2two
4. two2
5. secret word
6. my#variable
Are the identifiers secretNum and secretnum the same? ³
In Java, what is the difference between the statement System.out.print(...) and System.out.println(...)? ⁴

Debugging exercise

In VS Code, select File->New Text File, which will open up an empty editor window. It will initially have a name that is something like Untitled-1.
Select File->Save, and give the file the following name:
```
Section1.java
```
Important: When naming a Java file, the case of the letters matters. Make sure to use the exact combination of upper-case and lower-case letters that we specify. For this file, make sure to begin with an upper-case S.

Copy and paste the following buggy code into the editor window for Section1.java:

Public Class section1 {
    public static main(String args) {
        System.out.println(Go Crimson);
        System.out.pritnln("S-111 is the best"!);
            System.out.println("///Are you having fun?\\\");
        System.out.println()

        System.println("Bye!";
    {
}

Identify all of the bugs in the program and fix them. ⁵

Note: VS Code can help you to identify the bugs. Use the Terminal->New Terminal menu option, which should open a window known as a Terminal below the editor window. Click on the word PROBLEMS at the top of the Terminal window, which should reveal a list of syntax errors in the code.

Keep making the necessary changes until no more problems remain and you are able to run the program.

Other Java exercises

Write a System.out.println(...) statement that would produce the following output: ⁶
```
Joe said, "We're my teaching assistant's favorite class!"
```
Write a Java class called HarvardSpirit that produces the following output. Make sure your HarvardSpirit.java file has a block comment at the top listing the file name, the author, and a short description of the file. ⁷
```
/////////////
HARVARD S-111
\\\\\\\\\\\\\
```

The following StickFigure class draws a stick figure graphic using only text characters. Copy this code into a new file in VS Code, then write a method drawFigure() that draws an entire stick figure. Then change the main() method so that it calls drawFigure() twice. ⁸

public class StickFigure {
    public static void main(String[] args) {
        System.out.println("\\ O /");
        System.out.println(" \\|/");
        System.out.println("  |");
        System.out.println(" / \\");
        System.out.println("/   \\");

        System.out.println();
        System.out.println();

        System.out.println("\\ O /");
        System.out.println(" \\|/");
        System.out.println("  |");
        System.out.println(" / \\");
        System.out.println("/   \\");
    }
}

What output is produced by the following program? Note: Don’t just copy the code into VS Code! First, trace the program by hand, and then you can verify your answer by creating a new file for the program in VS Code and running it. ⁹

public class Blastoff {
    public static void main(String[] args) {
        three();
        two();
        one();

        System.out.println("blastoff");
    }

    public static void one() {
        three();
        System.out.println("one");
    }

    public static void two() {
        one();
        System.out.println("two");
        three();
    }

    public static void three() {
        System.out.println("three");
    }
}

An identifier is a name used in code to refer to a method, class, or other construct. Programmers have control over what identifiers to use when writing a program. ↩
SECRET_NUMBER and two2 are valid identifiers. average?num is invalid because it contains a ? character. 2two is invalid, since it starts with a number. secret word is invalid because it contains a space. my#variable is invalid because it contains a # character. ↩
secretNum and secretnum are not the same, since identifiers are case-sensitive. Here, secretNum and secretnum would refer to different things. ↩
System.out.println(...) automatically includes a newline character (\n) after the string, whereas System.out.print(...) does not include a newline. ↩

The following is a fixed version of the class:

public class Section1 {
    public static void main(String[] args) {
        System.out.println("Go Crimson");
        System.out.println("S-111 is the best!");
        System.out.println("///Are you having fun?\\\\\\");
        System.out.println();

        System.out.println("Bye!");
    }
}

↩

System.out.println("Joe said, \"We're my teaching assistant's favorite class!\""); ↩
HarvardSpirit.java ↩
StickFigure.java ↩

The output is as follows:

three
three
one
two
three
three
one
blastoff

↩

Last updated on June 25, 2025.