CSCI A201/A597

Lecture Notes 19

We can add a second method definition that will print a custom greeting, provided that we pass the adequate information to it. Details on how this works are provided in the book on pages 100-111 and will also be provided in class today. Here's the code:

frilled.cs.indiana.edu%ls -ld dgerman7.java
-rw-------   1 dgerman       400 Mar 21 10:04 dgerman7.java
frilled.cs.indiana.edu%cat dgerman7.java
import element.*;
import java.awt.Color;

public class dgerman7 {
    public static void main(String[] args) {
	Library.printGreeting(); 
        Library.printCustomGreeting("Hello again!");  
    } 
} 

class Library {
    public static void printGreeting() {
	System.out.println("Hello"); 
    }
    public static void printCustomGreeting(String greeting) {
	System.out.println(greeting); 
    }
} 
frilled.cs.indiana.edu%javac dgerman7.java
frilled.cs.indiana.edu%java dgerman7
Hello
Hello again!
frilled.cs.indiana.edu%

Inside the new procedure greeting is like a variable and is called a formal parameter. Any String that we pass to this new method at the time we invoke it will be known as greeting inside the body of the method. (The body of the method is always in between the curly braces, as was the case with main, or some for loops and while statements). Let's now return to homework 7.

In class I may be developing things using Symantec, for a change. You will see that the editor is nice, and the overall edit compile and run loop is also well supported. However we should always be prepared to use javac and java to compile and run.

Getting back to homework 7 can be done as follows.

import element.*;
import java.awt.Color;

public class dgerman7 {
    public static void main(String[] args) {
        Library.printCustomGreeting("Welcome to Homework Seven!"); 
        DrawingWindow d = new DrawingWindow();  
        // now we are ready to draw in d...
    } 
} 

class Library {
    public static void printGreeting() {
	System.out.println("Hello"); 
    }
    public static void printCustomGreeting(String greeting) {
	System.out.println(greeting); 
    }
}

So let's start by defining some variables in main then drawing the grid.

import element.*;
import java.awt.Color;

public class dgerman7 {
    public static void main(String[] args) {
        // Greet the user. Where does this greeting get printed? 
        Library.printCustomGreeting("Welcome to Homework Seven!"); 
        // Create a drawing window 
        DrawingWindow d = new DrawingWindow(); 
        // Now we are ready to draw in d...
        int xL,     // Coordinate of left vertical border of grid 
	    yL,     // Coordinate of top horizontal border of grid  
	            // (xL, yL) is top left corner of grid 
	    cols,   // Number of columns we want in grid 
	    lines,  // Number of lines we want in grid 
	    width,  // Width in pixels of a cell in the grid 
	    height; // Height in pixels of a cell in the grid 
        // Initialize the declared variables, one by one.
        xL = 20; 
	yL = 30;     // Top left corner coordinates are arbitrary 
	cols = 11;
	lines = 7;   // Matches the example shown in diagram. 
	width = 12;
	height = 12; // Cells in grid will actually be squares. 
        // By default a drawing window's size is 200 x 200 pixels.
        Library.drawGrid(d, xL, yL, cols, lines, width, height); 
    } 
} 

class Library {
    public static void printGreeting() {
	System.out.println("Hello"); 
    }
    public static void printCustomGreeting(String greeting) {
	System.out.println(greeting); 
    }
    public static void drawGrid(DrawingWindow dW, // The Window
				int x,            // xL
                                int y,            // yL
				int c,            // cols
				int l,            // lines
				int w,            // cell width
				int h) {          // cell height
	System.out.println(" I should be drawing the grid now ... "); 
    }
} 

The first step in our development process is to make it very explicit that we want to first draw the grid. We set aside a separate procedure (or method) in the Library class and give it a reasonable name: drawGrid. As part of the design process we acknowledge that we need to pass this procedure a lot of information for it to be able to draw what we want. We pass it everything we have defined thus far in main, as variables declared in main will not be know outside its body. The new procedure definition will have to match the number and type of arguments, but can use different names for them, which is what we have done in our example. The body of the procedure is empty now, but for debugging purposes we have placed a println statement in it to see that the procedure is executed (and the message gets printed). Our next step is to flesh out the body of the procedure.

import element.*;
import java.awt.Color;

public class dgerman7 {
    public static void main(String[] args) {
        // Greet the user. Where does this greeting get printed? 
        Library.printCustomGreeting("Welcome to Homework Seven!"); 
        // Create a drawing window 
        DrawingWindow d = new DrawingWindow(); 
        // Now we are ready to draw in d...
        int xL,     // Coordinate of left vertical border of grid  
	    yL,     // Coordinate of top horizontal border of grid 
	            // (xL, yL) is top left corner of grid 
	    cols,   // Number of columns we want in grid 
	    lines,  // Number of lines we want in grid 
	    width,  // Width in pixels of a cell in the grid 
	    height; // Height in pixels of a cell in the grid 
        // Initialize the declared variables, one by one.
        xL = 20; 
	yL = 30;     // Top left corner coordinates are arbitrary
	cols = 11;
	lines = 7;   // Matches the example shown in diagram. 
	width = 12;
	height = 12; // Cells in grid will actually be squares.
        // By default a drawing window's size is 200 x 200 pixels.
        Library.drawGrid(d, xL, yL, cols, lines, width, height); 
    } 
} 

class Library {
    public static void printGreeting() {
	System.out.println("Hello"); 
    }
    public static void printCustomGreeting(String greeting) {
	System.out.println(greeting); 
    }
    public static void drawGrid(DrawingWindow dW, // The Window
				int x,            // xL
                                int y,            // yL
				int c,            // cols
				int l,            // lines
				int w,            // cell width
				int h) {          // cell height
	System.out.println(" Drawing of grid starts... "); 
        for (int i = 0; i < l; i++) {
	    for (int j = 0; j < c; j++) {
		Rect r = new Rect(x + j * w, y + i * h, w, h); 
		dW.draw(r); 
	    } 
            System.out.println(" Done with line: " + i); 
	}  

    }
} 

import element.*;
import java.awt.Color;

public class dgerman7 {
    public static void main(String[] args) {
        Library.printCustomGreeting("Welcome to Homework Seven!"); 
        DrawingWindow d = new DrawingWindow(); 
        int xL = 20, yL = 30, cols = 11, lines = 7, width = 12, height = 12; 
        Library.drawGrid(d, xL, yL, cols, lines, width, height); 
    } 
} 

class Library {
    public static void printGreeting() {
	System.out.println("Hello"); 
    }
    public static void printCustomGreeting(String greeting) {
	System.out.println(greeting); 
    }
    public static void drawGrid(DrawingWindow dW, // The Window
				int x,            // xL
                                int y,            // yL
				int c,            // cols
				int l,            // lines
				int w,            // cell width
				int h) {          // cell height
	System.out.println(" Drawing of grid starts... "); 
        for (int i = 0; i < l; i++) {
	    for (int j = 0; j < c; j++) {
		Rect r = new Rect(x + j * w, y + i * h, w, h); 
		dW.draw(r); 
		Library.wait1second();  
	    } 
            System.out.println(" Done with line: " + i); 
	} 

    }
    public static void wait1second() {
	long now, then; 
	now = System.currentTimeMillis(); 
        then = now + 1000; 
        while (System.currentTimeMillis() < then) {
	    // do nothing (keep checking)) 
	} 
    } 
} 

Let's draw the two buttons erase and quit:

import element.*;
import java.awt.Color;

public class dgerman7 {
    public static void main(String[] args) {
        Library.printCustomGreeting("Welcome to Homework Seven!"); 
        DrawingWindow d = new DrawingWindow(); 
        int xL = 20, yL = 30, cols = 11, lines = 7, width = 12, height = 12; 
        Library.drawGrid(d, xL, yL, cols, lines, width, height);   
        Rect erase = new Rect(10, 10, 30, 10); 
        Rect quit  = new Rect(10 + 30, 10, 30, 10); 
        Library.drawButtons(d, erase, quit); 
    } 
} 

class Library {
    public static void printGreeting() {
	System.out.println("Hello"); 
    }
    public static void printCustomGreeting(String greeting) {
	System.out.println(greeting); 
    }
    public static void drawGrid(DrawingWindow dW, // The Window
				int x,            // xL
                                int y,            // yL
				int c,            // cols
				int l,            // lines
				int w,            // cell width
				int h) {          // cell height
	System.out.println(" Drawing of grid starts... "); 
        for (int i = 0; i < l; i++) {
	    for (int j = 0; j < c; j++) {
		Rect r = new Rect(x + j * w, y + i * h, w, h); 
		dW.draw(r); 
		// Library.wait1second(); 
	    } 
            System.out.println(" Done with line: " + i); 
	} 

    }
    public static void wait1second() {
	long now, then; 
	now = System.currentTimeMillis(); 
        then = now + 1000; 
        while (System.currentTimeMillis() < then) {
	    // do nothing (keep checking)) 
	} 
    } 
    public static void drawButtons(DrawingWindow d, Rect e, Rect q) {
	d.draw(e); 
	d.setForeground(Color.blue); 
	d.fill(q); 
	d.setForeground(Color.black);
	d.draw(q); 
    }     
}