B2: Methods and Method Calls
CPSC 210
Slides designed by Felix Grund, based on Paul Carter’s slides
Learning Goals
- Identify the type of an object
- Identify a method call and the object on which it is called
- Identify a method definition
- Navigate a sequence of method calls
- Draw a call graph starting from a specified method
(Demo)
Example: Space Invaders (1)
Pod Activity (Do in Groups of 3-5)
- Each student should clone the B02-SpaceInvadersBase repository
- Make sure you can run the game
- Play the game ONCE and see who can get the highest score
Example: Space Invaders (2)
Package Relationship Diagram
SpaceInvaders
ScorePanel
GamePanel
SIGame
Invader
Missile
Tank
ui
model
Package Relationship Diagram
Tank Code Example
Tank myTank;
myTank = new Tank(400);
myTank.faceLeft();
myTank.move();Declare new variable myTank of type Tank
Assign new Tank object to variable
Call faceLeft method on Tank object
Call move method on Tank object
Class Example: Tank
Class
Methods
Attributes/Fields
Constructor
1
2
3
4
(View > Tool Windows > Structure)
From: Space Invaders
Important Notes: Call Graphs
- If methodA calls methodB more than once, we record the call only once on the call graph
- However, if methodA and methodB each make a call to methodC, we record the call from methodA to methodC and the call from methodB to methodC
- Unless stated otherwise in the question, you should include calls to constructors and the first level of calls to methods in the Java library
Call Graph Example
Tank
move
Tank
handleBoundary
Tank.move
GamePanel.drawMissiles
Pod Activity (Do in Groups of 3-5)
- Start from GamePanel.drawMissiles and draw the Call Graph
- In VS Code, the shortcuts for looking at the implementation and usage of a method are different from in the video!
- Make sure all members of the pod know how to do this (macOS, Windows, etc...)
GamePanel.drawMissiles
GamePanel.drawMissiles
GamePanel
drawMissiles
SIGame
getMissiles
GamePanel
drawMissile
Missile
getX
Missile
getY
Lecture Lab
Note: constructors are just methods in call graphs, e.g.
Person
Person