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If you define any constructors, the default constructor will no longer be provided automatically. Therefore, if a constructor that takes no arguments willever be needed for your new class, and you define one or more parameterized constructors, you must define the noarg constructor when you define your class.
A parameterized constructor for Worker
The class named Worker in this program defines a constructor that receives two incoming parameters, one of type int and the other of type boolean . It uses those two incoming parameters to initialize two instance variables of the new object.
Oops!
However, it does not define a constructor with no arguments in the formal argument list (commonly called a noarg constructor) .
Calling the missing noarg constructor
The following code in the main method of the controlling class attempts to instantiate two objects of the Worker class. The first call of the constructor passes no parameters to the constructor. Thus, it requires a noarg constructor in order to instantiate the object.
public class Ap118{
public static void main(String args[]){new Worker().display();
new Worker(5,true).display();System.out.println();
}//end main()}//end class Ap118 A compiler error
Since there is no constructor defined in the Worker class with an empty formal argument list (and the default version is not provided) , the program produces the following compiler error.
Ap118.java:11: cannot resolve symbol
symbol : constructor Worker()
location: class Workernew Worker().display(); C. 0 0.0 false
All instance variables are initialized to default values
All instance variables are automatically initialized to default values if the author of the class doesn't take explicit steps to cause them to initialized toother values.
The default values
Numeric variables are automatically initialized to zero, while boolean variables are automatically initialized to false. Instance variables of type char are initialized to a Unicode value with all 16 bits set to zero. Reference variables are initialized to null.
A. Compiler Error
Pushing the compiler beyond its limits
Compared to many programming environments, the Java compiler is very forgiving. However, there is a limit to how far even the Java compiler iswilling to go to keep us out of trouble.
Initializing the value of a static variable
We can initialize the value of a static variable using an initialization expression as follows:
public static final MY_CONSTANT
= initialization expression; Important point
It is necessary for the compiler to be able to evaluate the initialization expression when it is encountered.
Illegal forward reference
This program attempts to use an initialization expression that makes use of the value of another static variable (myPI) that has not yet been established at that point in the compilation process. As a result, the program produces thefollowing compiler error under JDK 1.3.
Ap116.java:18: illegal forward reference
= 2 * myPI;^ 
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