Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

is intended to be used to initialize the data associated with objects of this class so
that they may be in a stable initial state when first created.
Constructors are invoked in a unique way: they must be called using the new
operator. So, upon invocation, a new instance of this class is automatically created
and its constructor is then called to initialize its instance variables and perform other
setup tasks. For example, consider the following constructor invocation (which is
also a declaration for the myFish variable):
Fish myFish = new Fish (7, "Wally");
A class can have many constructors, but each must have a different signature, that
is, each must be distinguished by the type and number of the parameters it takes.
The main Method
Some Java classes are meant to be used by other classes, others are meant to be
stand-alone programs. Classes that define stand-alone programs must contain one
other special kind of method for a class—the main method. When we wish to
execute a stand-alone Java program, we reference the name of the class that defines
this program by issuing the following command (in a Windows, Linux, or UNIX
shell):
java Aquarium
In this case, the Java run-time system looks for a compiled version of the
Aquarium class, and then invokes the special main method in that class. This
method must be declared as follows:
public static voidmain(String[] args){
}
// main method body …
The arguments passed as the parameter args to the main method are the
commandline arguments given when the program is called. The args variable is an
array of String objects, that is, a collection of indexed strings, with the first string
being args[0], the second being args[1], and so on. (We say more about arrays in
Section 1.5.)
Calling a Java Program from the Command Line
Java programs can be called from the command line using the java command,
followed by the name of the Java class whose main method we wish to run, plus
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