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 the interpreter returns the error:
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorldApp.java.
Answer 3: Check your classpath. The interpreter cannot find your class.Exercises
Exercise 1: Change theHelloWorldApp.java
program so that it displaysHola Mundo!
instead ofHello World!
.Answer 1: This is the only line of code that must change:
final JLabel label = new JLabel("Hola Mundo");Exercise 2: Get the following file from the online Tutorial:
Useless.java
Compile and run this program. What is the output?
Answer 2:This program prints out your default locale; for example,
indicates U.S. English.en_USExercise 3: 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 3: Here's the error you get when you try to compile the program:
To fix this mistake, you need to close the quotation marks around the string. Here is the correct line of code: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 errorsSystem.out.println("Hello World!"); //Display the string.
Exercise 4: Download the following two source files:
Compile the files, and then run the resulting program. What is the output? If you have trouble compiling the files but have successfully compiled before, try unsetting theFirstClass.java
SecondClass.java
CLASSPATH
environment variable, and then compile again.Answer 4: The key is to compile and run the
SecondClass
.FirstClass
does not have amain
method, so it cannot run independently.Here's the output (if your locale is U.S. English):
English (United States)