bit 115: introduction to programming professor: dr. baba kofi weusijana (say doc-tor...

BIT 115: Introduction To Programming


Professor: Dr. Baba Kofi Weusijana

(say Doc-tor Way-oo-see-jah-nah,

Doc-tor, or Bah-bah)

[email protected]

http://edutek.net/cascadia/bit115

BIT 115: Introduction To Programming 2

Quiz 11

•https://catalysttools.washington.edu/webq/survey/babaw/55000

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Review of Quiz 10 Results

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Today• Finish polymorphism example• Predicate (Helper) methods

– the return keyword

• Nested while loops

• Next class: – Non-robotic software– Modifiers (public, private, protected)– Debugging & unit testing– Programs stored in multiple files


Homework Assignments & Journals

• J#3 due today• J#4 & A03 due Mon 5/19


Polymorphism benefit

• Can refer to the superclass as the type of an object of an extended class– Change the type of joe in

ICE_10_Demo_1.java from SpinningRobot to Robot but don’t change new SpinningRobot(...)

– This will be very helpful when we start putting objects into other objects such as arrays and collections

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Nested Loops

• Suppose we want to place Things in a row, we can do that with a while loop and a row integer variable– Notice : only 1 dimensional output

• What if you wanted to also place Things across columns (2D output)?– inside the row while loop, have a column while loop

• We call this nesting– you can nest loops, if statements, select cases, etc.

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ICE Part 2: Nested Loops

• With Eclipse set breakpoint on line 12 of NestedWhile.java

• Trace the code in the debugger and watch the changes

• If we wanted to, we could nest 3 loops inside each other, etc

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Queries, Predicates, Integers in tests• A query method is a question asking

method– Used to figure out something about the current

state of the program– Queries SHOULDN'T have side effects:

shouldn’t change the state of the object• for example, when a robots’ query method ends, the

robot should be in the same situation it was when the method was called

• Example: public int countThingsInBackpack() in the becker.robots.Robot class 9


Predicates

• Predicate methods are true/false (yes/no) queries– Return a boolean value (true or false)– Usually have “is” in their name

• For example in becker.robots.Robot:– frontIsClear– isBesideThing

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Return• return can be used to indicate what

answer the method wants to give• It will immediately stop the method from

going any further, and instead return to whatever method called the current method

• Example:public boolean isTrue(){ return true;}

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Return

• Normally, you'd combine return with some other logic to create a more useful bit of functionality:

public boolean isRobotOnAvenueFive(){if (this.getAvenue() == 5){return true;}else{return false;}}

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Return• You can also directly return anything that will be true/false when

the program is run:public boolean isRobotOnAvenueFive(){return (this.getAvenue() == 5);}

• Return can also be used in void methods to indicate that you simply want to stop the method & return to the callerpublic void doNothing()

{return;System.out.println(“Never say this.”);} 1

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Using return just to stop a method/** This will put down as many as five things, in a row. The method will stop if the robot doesn't have 5 Things to place */public void placeFiveThings(){

int counter = 0;while(counter < 5){if(this.countThingsinBackPack() > 0){this.putThing();}else{

// This will simply stop the current method from runningreturn;}}} 1

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ICE Part 1, with the sample test code

• FileName.java

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Integer tests

• These queries return int numbers:int getAvenue();

int getStreet();

Direction getDirection(); //one of Directions.NORTH, Directions.SOUTH, etc

int getSpeed();

• Note that these are all public methods• Integer tests are not very useful unless we

can compare them to other things & do some simple math on them

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• ICE Part 3: Variable Design

• Discuss:– What are good answers?

• TYPO:– Students DO NOT need to turn in a MS Word

doc, but good quiz practice

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ICE Parts 4 & 5

• Note: You must fix class naming problem by making packages

• Can turn in as late as by class on Monday 5/12 to the Java Code Critic

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bit 115: introduction to programming professor: dr. baba kofi weusijana (say doc-tor...

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