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-Read all 4 questions before writing anything

-answer the easiest question 1st

-most times question 1 is the easiest

-see if part B calls part A and so on

-many times part C consists of A and B calls

-write something on every question

-write legibly / use PENCIL!!!!!!!!!!

-keep track of your time


-When writing methods

-use parameter types and names as provided

-do not redefine the parameters listed

-do not redefine the methods provided

-return from all return methods

-return correct data type from return methods


-When writing a class or methods for a class

-know which methods you have

-know which instance variables you have

-check for public/private on methods/variables




-When extending a class

-know which methods the parent contains

-have the original class where you can see it

-make sure you have super calls


-make super calls in sub class methods as needed


-When extending abstract / implementing interface






-implement all abstract methods in sub class


-When writing GridWorld question

-use the GridWorld quick reference

-use original method code when overidding

-use Bug and BoxBug code if extending Bug

-use Critter and ChameleonCritter code if extending Critter

-use Critter and Bug for extends demo

-use Critter for ArrayList and Math.random() demo

-use GW quick reference on the entire AP test


ArrayList of References / Objects – get,set,remove,add,size – levels of abstraction

Matrix / 2 D Array – nested loops, GridWorld ( grid )

GridWorld or Make a Class– location, actor, bug, critter, grid, super, abstract

String / Array Question – find biggest, find smallest, etc.


One question on the A test free response is usually an array or string question.

CustomerSortRobotReservationStringCoder


This question usually involves an array and / or a string and many times has sorting and searching components.


0 1 2 3 4 5 6 7 8 9

nums 0 0 0 0 0 0 0 0 0 0

int[] nums = new int[10]; //Java int array

An array is a group of items all of the same type which are accessed through a single identifier.


0 1 2 3 4 5 6

s

String s = "compsci";

A string is a group of characters.The first character in the group is at spot 0.

c o m p s c i


Stringfrequently used methods

Name Use

substring(x,y)

returns a section of the string from x to y not including y

substring(x) returns a section of the string from x to length-1

length() returns the # of chars

charAt(x) returns the char at spot x

indexOf(c) returns the loc of char c in the string, searching from spot 0 to spot length-1

lastIndexOf(c)

returns the loc of char c in the string, searching from spot length-1 to spot 0


Stringfrequently used methods

Name Useequals(s) checks if this string has same chars as

s

compareTo(s) compares this string and s for >,<, and ==

trim() removes leading and trailing whitespace

replaceAll(x,y) returns a new String with all x changed to y

toUpperCase() returns a new String with uppercase chars

toLowerCase() returns a new String with lowercase chars

public int limitAmplitude(int limit) { int cnt = 0; for ( int i = 0; i < samples.length; i++ ) { if ( samples[i] < -limit ) { samples[i] = -limit; cnt++; } if ( samples[i] > limit ) { samples[i] = limit; cnt++; } } return cnt;}

public void trimSilenceFromBeginning() { int i = 0; while ( samples[i] == 0 ) { i++; }

int[] ray = new int[ samples.length – i ]; for (int j = 0; j < ray.length; j++) { ray[j] = samples[j+i]; } samples = ray;}


One question on the A test free response will require that you create a class. Sometimes you have to extend an abstract class or implement an interface. Other times, you will extend another class like Critter.


Locationfrequently used methods

Name UseLocation(row, col)

creates a new row,col Location

getCol() gets the column value for this location

getRow() gets the row value for this location

import info.gridworld.grid.Location;


Locationfrequently used fields

Name Use

NORTH indicates going north – value of 0

SOUTH indicates going south – value of 180

EAST indicates going east – value of 90

WEST indicates going west – value of 270

import info.gridworld.grid.Location;


Location locOne = new Location(2,1);Location locTwo = new Location(1,3);

out.println(locOne.getAdjacentLocation(Location.NORTH));out.println(locOne.getAdjacentLocation(Location.SOUTH));out.println(locOne.getAdjacentLocation(Location.EAST));out.println(locOne.getAdjacentLocation(Location.WEST));

OUTPUT(1, 1)(3, 1)(2, 2)(2, 0)

0,0 0,1 0,2 0,3 0,4

1,0 1,1 1,2 1,3 1,4

2,0 2,1 2,2 2,3 2,4

3,0 3,1 3,2 3,3 3,4


Location locOne = new Location(2,1);Location locTwo = new Location(1,3);

out.println(locOne.getDirectionToward(locTwo));

OUTPUT45

0,0 0,1 0,2 0,3 0,4

1,0 1,1 1,2 1,3 1,4

2,0 2,1 2,2 2,3 2,4

3,0 3,1 3,2 3,3 3,4


Actorfrequently used methods

Name Use

Actor() creates new blue north bound actor

act() reverses the direction for actor

getColor() gets the actor’s color

getDirection() gets the actor’s direction

getLocation() gets the actor’s location

setColor(col) sets the actor’s color to col

setDirection(dir) sets the actor’s direction to dir

moveTo(loc) moves the actor to new location loc


Actorfrequently used methods

Name UseputSelfInGrid(grid, loc)

put this actor in grid at loc

removeSelfFromGrid()

takes this actor out of the grid

getGrid() gets the grid which contains this actor

toString() gets actor data as a String

import info.gridworld.actor.Actor;


ActorWorld world = new ActorWorld();Actor dude = new Actor();dude.setColor(Color.GREEN);dude.setDirection(Location.SOUTH);Location loc = new Location(2,2);world.add(loc, dude);world.show(); What happens if you

click on an empty location?


Gridabstract methods

Name Useget(loc) returns the ref at location loc

getEmptyAdjacentLocations(loc) gets the valid empty locs in 8 dirs

getNeighbors(loc) returns the objs around this

getNumCols() gets the # of cols for this grid

getNumRows() gets the # of rows for this grid

getOccupiedAdjacentLocations(loc)

gets the valid locs in 8 dirs that contain objs

getOccupiedLocations() gets locs that contain live objs

getValidAdjacentLocations(loc) gets the valid locs in 8 dirs

isValid(loc) checks to see if loc is valid

put(loc, obj) put the obj in grid at location loc

remove(loc) take the obj at location loc out of the grid

import info.gridworld.grid.Grid;


Grid is an interface that details thebehaviors expected of a Grid.

Grid was designed as an interface because many different structures could be used to store the grid values.

An interface works perfectly due to the large number of unknowns.


Grid<String> grd;grd = new BoundedGrid<String>( 4, 5 );

grd.put( new Location( 2, 2 ) , "CAT" );

grd.put( new Location( 1, 3 ) , "DOG" );

System.out.println( grd.get( new Location( 0, 0 ) );

System.out.println( grd.get( new Location( 2, 2 ) );

OUTPUTnullCAT

null null null null null

null null null DOG null

null null CAT null null

null null null null null


Bug extends Actor

frequently used methodsName Use

act() move if possible or turn

getColor() gets the bug’s color

getDirection() gets the bug’s direction

getLocation() gets the bug’s location

setColor(col) sets the bug’s color to col

setDirection(dir) sets the bug’s direction to dir

import info.gridworld.actor.Bug;


Bug extends Actor

frequently used methods – Bug onlyName Use

Bug() make a new red bug going north

Bug(color) make a new color bug

act() move if possible or turn

canMove() check to see if a move is possible

move() move forward and leave a flower

turn() turn 45 degrees without movingimport

info.gridworld.actor.Bug;


ActorWorld world = new ActorWorld();

Bug dude = new Bug();world.add(new Location(3,3), dude);

Bug sally = new Bug(Color.GREEN);sally.setDirection(Location.SOUTHEAST);world.add(new Location(2,2), sally);

Bug ali = new Bug(Color.ORANGE);ali.setDirection(Location.NORTHEAST);world.add(new Location(1,1), ali);

world.show();


The bug act method looks to see if a move is possible by calling canMove.

canMove looks at the location in front of this bug to see if it is empty or if it contains a flower.

canMove returns true or false.


The bug act method calls move if canMove returns true.

move calls moveTo to move the bug to the location in front of this bug. move leaves a flower in the old location.


The bug act method calls turn if canMove returns false.

turn changes the direction of the bug by 45 degrees to the right.


Critter extends Actor

frequently used methodsName Use

getColor() gets the critter's color

getDirection() gets the critter's direction

getLocation() gets the critter's location

setColor(col) sets the critter's color to col

setDirection(dir) sets the critter's direction to dir

import info.gridworld.actor.Critter;


Critter extends Actor

frequently used methods – Critter specific

Name Useact() calls the methods listed below

getActors() gets all actors around this location

processActors(actors) do something to actors sent in

getMoveLocations() gets list of possible move locs

selectMoveLocation(locs)

picks loc to move to

makeMove(loc) moves this critter to locimport info.gridworld.actor.Critter;


if no grid present – stop

call getActors to get list of actors to proces processActors received from getActors

call getMoveLocations to get a list of locations

to which the critter might movecall selectMoveLocation to select new location

move to the new loc


The getActors method returns an ArrayList containing all of the actors around this critter using the 4 cardinal(N,S,E,W) and 4 intercardinal directions(NE, NW, SE, SW).

In order to change which actors are returned by getActors, override the method and provide a different method of selecting actors.

getActors must not modify any actors.getActors must not modify any actors.


A typical Abstract/Interface questionrequires that a class be written that extends the abstract class or implements the interface and that all abstract method(s) be implemented.


Abstract classes are used todefine a class that will be used only to build new classes.

No objects will ever be instantiated from an abstract class.


Mammal (abstract class)

Human Whale Cow


Any sub class that extends asuper abstract class must implement all methods defined as abstract in the super class.


abstract class Monster{ private String myName;

public Monster() { myName =""; }

public Monster(String name) { myName =name; }

public String getName() { return myName; }

public abstract void talk( );

public String toString() { return myName + "\n"; }}


Why define talk as abstract?public abstract void talk( );

Does each Monster saythe exact same thing?


class Vampire extends Monster{ public Vampire( String name ) { super(name); }

public void talk() { out.println("Vampire " + getName() + " say \"I want to drink your blood!\""); }}


public abstract class APlus{ public APlus(int x) //constructor code not shown

public abstract double goForIt();

//other fields/methods not shown}

PetItem


public class PassAPTest extends APlus{ public PassAPTest(int x) { super(x); }

public double goForIt() { double run=0.0; //write some code - run = x*y/z return run; }


public abstract class APlus{ public APlus(int x) //constructor code not shown

public abstract double goForIt();



public interface Exampleable{ int writeIt(Object o); int x = 123;}

Methods are public abstract!Variables are public static final!


public interface Exampleable{ public abstract int writeIt(Object o); public static final int x = 123;}

Methods are public abstract!Variables are public static final!


An interface is a list of abstract methods that must be implemented. An interface may not contain any implemented methods.

Interfaces cannot have constructors!!!


Interfaces are typically used when you know what you want an Object to do, but do not know how it willbe done.

If only the behavior is known, usean interface.


Abstract classes are typically used when you know what you want an Object to do and have a bit of anidea how it will be done.

If the behavior is known and someproperties are known, use an abstractclass.

public class AttractiveCritter extends Critter {

public ArrayList<Actor> getActors() { ArrayList<Actor> stuff; stuff = new ArrayList<Actor>(); for ( Location loc : getGrid().getOccupiedLocations() ) { if ( !loc.equals(getLocation()) ) stuff.add( getGrid().get(loc) ); } return stuff; } You must know

ArrayList!

public void processActors(ArrayList<Actor> actors) { for (Actor a : actors) { Location loc = a.getLocation(); int dir = loc.getDirectionToward( getLocation() ); Location x = loc.getAdjacentLocation(dir); if (getGrid().get( x ) == null) { a.moveTo( x ); } }}

You must know ArrayList!


A typical ArrayList question involves putting something into an ArrayList and removing something from an ArrayList.


Arraylist is a class that houses anarray.

An ArrayList can store any type.

All ArrayLists store the first referenceat spot / index position 0.


0 1 2 3 4 5 6 7 8 9

nums 0 0 0 0 0 0 0 0 0 0

int[] nums = new int[10]; //Java int array

An array is a group of items all of the same type which are accessed through a single identifier.


ArrayListfrequently used methods

Name Use

add(item) adds item to the end of the list

add(spot,item) adds item at spot – shifts items up->

set(spot,item) put item at spot z[spot]=item

get(spot) returns the item at spot return z[spot]

size() returns the # of items in the list

remove() removes an item from the list

clear() removes all items from the list

import java.util.ArrayList;


List ray = new ArrayList(); ray.add("hello");ray.add("whoot");ray.add("contests");out.println(((String)ray.get(0)).charAt(0));out.println(((String)ray.get(2)).charAt(0));

ray stores Object references.

OUTPUT

hc


List<String> ray;ray = new ArrayList<String>(); ray.add("hello");ray.add("whoot");ray.add("contests");out.println(ray.get(0).charAt(0));out.println(ray.get(2).charAt(0));

ray stores String references.

OUTPUT

hc


int spot=list.size()-1;while(spot>=0){

if(list.get(spot).equals("killIt")) list.remove(spot);

spot--;

}


for(int i=list.size()-1; i>=0; i--){

if(list.get( i ).equals("killIt")) list.remove( i );

}


int spot=0;while(spot<list.size()){

if(list.get(spot).equals("killIt")) list.remove(spot); else spot++;

}

public int nextTankToFillA(int threshold) { int min = filler.getCurrentIndex(); for (int i = 0; i < tanks.size(); i++) { int curr = tanks.get(i).getFuelLevel() ; int min = tanks.get(min).getFuelLevel(); if ( curr <= threshold && curr < min ) { min = i; } } return min;}

You must know ArrayList!

public void moveToLocation(int locIndex){ if ( filler.getCurrentIndex() > locIndex) { if ( filler.isFacingRight()) { filler.changeDirection(); } filler.moveForward(filler.getCurrentIndex() - locIndex); } if (filler.getCurrentIndex() < locIndex) { if (!filler.isFacingRight()) { filler.changeDirection(); } filler.moveForward(locIndex - filler.getCurrentIndex()); }} You must know

ArrayList!


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One question on the A test free response will require you to manipulate a 2-dimensional array or a GridWorld grid.


0 1 2

0 0 0

int[][] mat = new int[3][3];

A matrix is an array of arrays.

0 0 0

0 0 0

0 1 2


int size = 40;

int[][] mat = {{5,7,9,2},{5,3,4,6},{7,0,8,9}};

int[][] intMat = new int[size][size];//intMat is filled with zeros - 0s


String[][] words = new String[4][4];//words is filled with null

double[][] dMat = new double[3][3];//dMat is filled with 0.0


int[][] mat = {{5,7,9,2,1,9},{5,3,4},{3,7,0,8,9}};

out.println(mat[2][1]);out.println(mat[1][2]);out.println(mat[0][3]);out.println(mat[2][4]);

OUTPUT

7429


int[][] mat = {{5,7,9,2,1,9},{5,3,4},{3,7,0,8,9}};

out.println(mat[7/4][0]);out.println(mat[1*2][2]);out.println(mat.length);out.println(mat[0].length);

OUTPUT

5036


0 2 0

int[][] mat = new int[3][3];mat[0][1]=2;


0 0 0

0 0 0

0 1 2

Whicharray?

Whichspot?

0 1 2


0 0 0 5 0

0 0 0 0 0

0 0 7 0 0

0 0 0 0 0

0 3 0 0 0

mat[2][2]=7;

mat[0][3]=5;

mat[4][1]=3

0 1 2 3 4

0

1

2

3

4


for( int r = 0; r < mat.length; r++){ for( int c = 0; c < mat[r].length; c++) {

mat[r][c] = r*c; }}

0 0 0

0 1 2

0 2 4if mat was 3x3


//start //stop //incrementfor(outer=1; outer<=2; outer++){

}

OUTPUT1 11 2

//start //stop //increment for(int inner=1; inner<=2; inner++) out.println(outer + " " + inner); out.println();

OUTPUT1 11 2

2 12 2

int outer=1;


0 1 2

0 0 0

int[][] mat = new int[3][3];


0 0 0

0 0 0

0 1 2

# of arrays

size of each array


int[][] mat = {{5,7},{5,3,4,6},{0,8,9}};

out.println(Arrays.toString(mat[0]));

out.println(Arrays.toString(mat[1]));

OUTPUT[5, 7][5, 3, 4, 6]


int[] nums = {1,2,3,4,5,6,7}; for(int r=0; r<nums.length; r++){ out.println(nums[r]); }

OUTPUT1234567

length returns the # of elements/items/spots in the array!!!


for(int r=0; r<mat.length; r++){

}

for(int c=0; c<mat[1].length; c++){ out.print(mat[1][c]);}out.println();

OUTPUT5 3 4 6

int[][] mat = {{5,7},{5,3,4,6},{0,8,9}};

for(int c=0; c<mat[r].length; c++){ out.print(mat[r][c]);}out.println();

OUTPUT5 75 3 4 60 8 9


int[][] mat = {{5,7},{5,3,4,6},{0,8,9}};

for( int[] row : mat ){ for( int num : row ) { System.out.print( num + " "); } System.out.println();}

OUTPUT5 75 3 4 60 8 9

private void fillBlock(String str) { int pos = 0; for (int r = 0; r < numRows; r++ ) for (int c = 0; c < numCols; c++ ) { if (pos < str.length()) { letterBlock[r][c] = str.substring(pos, pos+1); pos++; } else{ letterBlock[r][c] = "A"; } }}

public String encryptMessage(String message) { String mess = ""; int sect = numRows * numCols; while (message.length() > 0) { if (sect > message.length()) sect = message.length();

fillBlock(message); mess += encryptBlock(); message = message.substring( sect ); } return mess;}


ArrayList of References / Objects – get,set,remove,add,size – levels of abstraction

Matrix / 2 D Array – nested loops, GridWorld ( grid )

GridWorld or Make a Class– location, actor, bug, critter, grid, super, abstract

String / Array Question – find biggest, find smallest, etc.


-Read all 4 questions before writing anything

-answer the easiest question 1st

-most times question 1 is the easiest

-see if part B calls part A and so on

-many times part C consists of A and B calls

-write something on every question

-write legibly / use PENCIL!!!!!!!!!!

-keep track of your time


-When writing methods

-use parameter types and names as provided

-do not redefine the parameters listed

-do not redefine the methods provided




-When writing a class or methods for a class

-know which methods you have

-know which instance variables you have





-When extending a class







-When extending abstract / implementing interface






-implement all abstract methods in sub class


-When writing GridWorld question

-use the GridWorld quick reference

-use original method code when overidding

-use Bug and BoxBug code if extending Bug

-use Critter and ChameleonCritter code if extending Critter

-use Critter and Bug for extends demo

-use Critter for ArrayList and Math.random() demo

-use GW quick reference on the entire AP test

© A+ Computer Science - . Visit us at Full Curriculum Solutions M/C Review Question Banks.

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