Converting a stand alone java file to a file that's part of a project package?
Sam Peterson’s Question:
I still don’t fully understand where I’m required to use the “public static void main(String[] args)” header within the .java files of a project. Do you need to put that header in every .java file of a package?
I have been following along with chapter 3 in my book, dragging and dropping downloaded stand alone book source files into my project’s package, but some of the .java files in my package don’t like that “public static void main(String[] args)” statement, even though my opening and closing curly braces are in the correct place. Here’s an example of one of those files (the ERROR(S) are described in the code’s comments):
public class Rectangle
{
public static void main(String[] args){
private double length;//ERROR: illegal start of expression
private double width;
/**
* Constructor
*/
public Rectangle(double len, double w)
{
length = len;
width = w;
}
/**
* The setLength method accepts an argument
* that is stored in the length field.
*/
public void setLength(double len)
{
length = len;
}
/**
* The setWidth method accepts an argument
* that is stored in the width field.
*/
public void setWidth(double w)
{
width = w;
}
/**
* The set method accepts two arguments
* that are stored in the length and width
* fields.
*/
public void set(double len, double w)
{
length = len;
width = w;
}
/**
* The getLength method returns the value
* stored in the length field.
*/
public double getLength()
{
return length;
}
/**
* The getWidth method returns the value
* stored in the width field.
*/
public double getWidth()
{
return width;
}
/**
* The getArea method returns the value of the
* length field times the width field.
*/
public double getArea()
{
return length * width;
}
}//end of: public static void main(String[] args)
}//end of: public class Rectangle ERROR: class, interface, or enum expected
The ERROR(S) came up after I added the “public static void main(String[] args)” to the existing Rectangle.java file. Any idea of why this occurs?
This occurs because You cannot have more than one main() method in a package. However overriding the main method is definitely allowed. What I mean is as, long the parameter number is differed you can override main() method.
public static void main(String[] args) {
.....
}
And somewhere else in other or same class, you can add such class
public static void main(String arg1, String arg2) {
.....
}
The ERROR: illegal start of expression is because you are using access modifier inside the method. Use all the access mofifier and variable declaration inside the class
public class Rectangle {
private double length;//ERROR: illegal start of expression
private double width;
public static void main(String[] args) {
....
}
}
The ERROR: class, interface, or enum expected is because the class Rectangle is only housing a static method, your all the methods and parameters are inside the static method called main()
Here is your code which will compile without an error.
