Answers to Questions and Exercises: Getting Started

Questions

Question 1: When you compile a program written in the Java programming language, the compiler converts the human-readable source file into platform-independent code that a Java Virtual Machine can understand. What is this platform-independent code called?

Answer 1: Bytecode.

Question 2: Which of the following is not a valid comment:

a. /** comment */
b. /* comment */
c. /* comment
d. // comment

Answer 2: c is an invalid comment.

Question 3: What is the first thing you should check if you see the following error at runtime:

Exception in thread "main" java.lang.NoClassDefFoundError:
HelloWorldApp.java.

Answer 3: Check your classpath. Your class cannot be found.

Question 4: What is the correct signature of the main method?

Answer 4: The correct signature is public static void main(String[] args) or public static void main(String... args)

Question 5: When declaring the main method, which modifier must come first, public or static?

Answer 5: They can be in either order, but the convention is public static.

Question 6: What parameters does the main method define?

Answer 6: The main method defines a single parameter, usually named args, whose type is an array of String objects.

Exercises

Exercise 1: Change the HelloWorldApp.java program so that it displays Hola Mundo! instead of Hello World!.

Answer 1: This is the only line of code that must change:

System.out.println("Hola Mundo!"); //Display the string.

Exercise 2: You can find a slightly modified version of HelloWorldApp here: HelloWorldApp2.java

The program has an error. Fix the error so that the program successfully compiles and runs. What was the error?

Answer 2: Here's the error you get when you try to compile the program:

HelloWorldApp2.java:7: unclosed string literal
        System.out.println("Hello World!); //Display the string.
                           ^
HelloWorldApp2.java:7: ')' expected
        System.out.println("Hello World!); //Display the string.
                                                                ^
2 errors

To fix this mistake, you need to close the quotation marks around the string. Here is the correct line of code:

 System.out.println("Hello World!"); //Display the string.