Difference between constructor & Methods if any ?

Question

In the below code I use the constructor ConstructorShirt1('M') to pass the value of M to the class ConstructorShirt1, but why do we have to do this, instead can we not just use a method and write the same thing in a method.
class ConstructorShirt1Test {
     public static void main (String args[]) {
ConstructorShirt1 constShirt = new ConstructorShirt1('M');
char colorCode;
          colorCode = constShirt.getColorCode();
System.out.println("Color Code: " + colorCode);
class ConstructorShirt1 {
private int shirtID = 0; // Default ID for the shirt
private String description = "-description required-"; // default
// The color codes are R=Red, B=Blue, G=Green, U=Unset
private char colorCode = 'U';
private double price = 0.0; // Default price for all items
private int quantityInStock = 0; // Default quantity for all items
public ConstructorShirt1(char startingCode) {
switch (startingCode) {
case 'R':
case 'G':
case 'B':
colorCode = startingCode;
break;
default:
System.out.println("Invalid colorCode. Use R, G, or B");
public char getColorCode() {
return colorCode;
} // end of class
So I am not clear what is the difference between constructor and methods if any ? or if not when to use a constructor and when to use a method.
I would be glad if somebody throws light on this topic.
PK

Answer 1

There shouldn't be any confusion on this one... a constructor is meant to create an instance of the class. It can also set the state of its member variables in the process, like the constructor you are using. The same can also be done by a method.
Wouldn't make much of a difference for simple programs, but this is more pertinent when it comes to designing classes. Like if the developer using the class needs to know what all states he has to set before he needs to do anything useful, then it is better to provide a constructor with some arguments for doing that.