1  public class Square {
  2  
  3    // Instance variable:
  4    protected double width;
  5    
  6    // Constructors:
  7    public Square(double width) {
  8      setWidth(width);
  9    }
 10    public Square() { } 
 11    
 12    // Encapsulate the instance variable:
 13    public void setWidth(double width) {
 14      this.width = width;
 15    }
 16    public double getWidth() {
 17      return width;
 18    }
 19    
 20    // Instance methods:
 21    public double perimeter() {
 22      return 4*width;
 23    }
 24    public double area() {
 25      return width*width;
 26    }
 27    
 28  }