Java Reference
In-Depth Information
The remainder of this first program consists of two closing braces. The first closing
brace ends the definition of the method
main
. The last closing brace ends the defini-
tion of the class named
FirstProgram
.
Self-Test Exercises
1. If the following statement were used in a Java program, it would cause something
to be written to the screen. What would it cause to be written to the screen?
System.out.println("Java is not a drink.");
2. Give a statement or statements that can be used in a Java program to write the fol-
lowing to the screen:
I like Java.
You like tea.
3. Write a complete Java program that uses
System.out.println
to output the fol-
lowing to the screen when run:
Hello World!
Note that you do not need to fully understand all the details of the program in order to
write the program. You can simply follow the model of the program in Display 1.1.
Byte-Code and the Java Virtual Machine
Most modern programming languages are designed to be (relatively) easy for people to
write and to understand. These languages that were designed for people to read are
called
high-level languages
. The language that the computer can directly understand
is called
machine language
. Machine language or any language similar to machine
language is called a
low-level language
.
A program written in a high-level language,
like Java, must be translated into a program in machine language before the program
can be run. The program that does the translating (or at least most of the translating)
is called a
compiler
and the translation process is called
compiling
.
high-level,
low-level, and
machine
languages
compiler
Compiler
A
compiler
is a program that translates a high-level-language program, such as a Java pro-
gram, into an equivalent low-level-language program.
One disadvantage of most programming languages is that the compiler translates the
high-level-language program directly into the machine language for your computer.
Since different computers have different machine languages, this means you need a
