The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
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.
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.