Questions

• Reading?
• Homework?
• Quiz?

Activity - Object reference

Record your participation in Piazza clicker question Lesson3 Q1

Given this definition

Rectangle rec = new Rectangle(100, 200, 50, 80);

what does the variable rec hold?

1. the object
2. the location of the object
3. the data in the object
4. can not be determined from the information given

 

Activity - Two references to the same object

Record your participation in Piazza clicker question Lesson3 Q2

Given this code

Rectangle block = new Rectangle(10, 20, 30, 50);
Rectangle block2 = block;
block2.grow(0, 10);
System.out.println(block.getHeight() + " : " + block2.getHeight());

What is printed? (Remember the grow method adds to both sides.)

1. 50.0 : 70.0
2. 70.0 : 70.0
3. 50.0 : 50.0
4. 70.0 : 50.0

 

Concept - Pass by value, pass by reference

• There is no pass by reference in Java. Everything is passed by value.
• What is passed is the value of the variable
• When the variable is of a primitive data type, its value is passed
  • its value is a number, a boolean, or a char
• When the variable is of type object reference, its value is passed
  • its value is the location of the object

Activity - Creating two rectangles with same values

Record your participation in Piazza clicker question Lesson3 Q3

What does this code print? (Remember the grow method adds to both sides.)

Rectangle tile1 = new Rectangle( 10, 30, 50, 100);
Rectangle tile2  = new Rectangle( 10, 30, 50, 100);
tile2.grow(5, 0);
System.out.println(tile1.getWidth() + " " +  tile2.getWidth());
  

1. 60 50
2. 50 50
3. 50 60
4. 60 60

Activity - String methods

Record your participation in Piazza clicker question Lesson3 Q4

What is printed here?

	   String farewell = "Goodbye, Moon";
	   farewell.toLowerCase();
	   farewell.replace("o", "");
	   System.out.println(farewell);
	   

1. goodbye, moon
2. gdbye, mn
3. Goodbye, Moon
4. none of the above

Activity - String methods

Record your participation in Piazza clicker question Lesson3 Q5

What is printed here?

	   String farewell = "Goodbye, Moon";
	   String copy = farewell.toLowerCase();
	   copy = copy.replace("o", "");
	   copy = copy.replace("e", "3");
	   System.out.println(copy);
	   System.out.println(farewell);

1. gdby3, mn
   gdby3, mn

2. gdby3, mn
   Goodbye, Moon

3. something else

Activity - Constructing graphics shapes

Record your participation in Piazza clicker question Lesson3 Q6

Draw a staircase like the one below. The upper left hand corner is at (20, 10). Each step is 20 pixels tall. The first step is 20 pixels wide. Each of the following steps is 20 pixels wider than the one above.

Here is a zip containing the frame and component classes needed for drawing in a graphical application. Make a project in your IDE and add them. You can use this same set of starter classes for any graphics project we do.

• Add code to the paintComponent method
• Follow these specifications
  • The upper left hand corner of the first step is at (20, 10).
  • Each step has a height of 20 pixels
  • Construct the top step first. It has a width of 20 pixels. Draw it in blue
  • Construct the second step next. What are its coordinates? It has a width of 40 pixels. Fill it with green
  • Construct the bottom step last. What are its coordinates? It has a width of 60 pixels. Fill it with magenta
  • Construct a circle inside the bounding rectangle of the top stair. Fill it with red
  • Construct a line from the top left hand corner of the top stair to the bottom right hand corner of the bottom stair. Draw it in black
• Use the 2D graphics package as explained in your text. Here is how to make the first step

        Rectangle step1 = new Rectangle(20, 10, 20, 20);
        g2.setColor(Color.BLUE);
        g2.draw(step1);