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)
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.
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.
