A+ Computer Science AP Review 2018 AP CS A EXAM

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© A+ Computer Science - www.apluscompsci.com Multiple Choice -answer the easiest question 1st -work through the test more than once -use the test to take the test -work more time intensive problems last -bubble answers on answer sheet as you go -answer every question -keep track of your time - 90 minutes © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 -return from all return methods -return correct data type from return methods © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 -check for public/private on methods/variables -make super calls in sub class methods as needed © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -When extending abstract / implementing interface -know which methods the parent contains -have the original class where you can see it -make sure you have super calls -check for public/private on methods/variables -make super calls in sub class methods as needed -implement all abstract methods in sub class © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response Topics Algorithms – ifs and loops ArrayList – get,set,remove,add,size Make a Class – Implement an Interface – create a class that implements an interface Arrays and Matrices – nested loops - array of arrays concepts © A+ Computer Science - www.apluscompsci.com

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Free Response Question 1 Algorithm / Logic © A+ Computer Science - www.apluscompsci.com © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Algorithm / Logic Algorithm problems often use array and strings, but like this year, they sometimes just use simple loops and method calls. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Algorithm / Logic for(int aplus=1; aplus<7; aplus+=2) { out.println("comp"); out.println( aplus ); } OUTPUT comp 1 comp 3 comp 5 This loop starts run at 1 and increments run by two each iteration. The loop will continue to run as long as run is less than 7. The loop will stop when the condition run<7 fails. The condition will fail when run equals 7. run begins with the value 1 Iteration 1 – print run(1) run = 1 + 2 Iteration 2 – print run(3) run = 3 + 2 Iteration 3 – print run(5) run = 5 + 2 The loop condition fails when run reaches the value 7 as 7 is not less than 7. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Algorithm / Logic OUTPUT 25 loop 20 loop 15 loop 10 loop int run=25; while(run>=10) { out.println(run); out.println("loop"); run=run-5; } As long as run is less than or equal to 10 ( run<=10 ), the loop will iterate. For each iteration, run is displayed, loop is displayed, and run is decreased by 5. run begins with the value 25 Iteration 1 – print(25) print(loop) run = 25-5 Iteration 2 – print(20) print(loop) run = 20-5 Iteration 3 – print(15) print(loop) run = 15-5 Iteration 4 – print(10) print(loop) run = 10-5 The loop condition fails when run reaches the value 5 as 5 is not greater than or equal to 10. © A+ Computer Science - www.apluscompsci.com

2018 Question 1 Part A public boolean simulate() { int temp = maxHops; int loc = 0; while( temp > 0 && loc >= 0 && loc < goalDistance ) loc = loc + hopDistance(); temp--; } if( loc >= goalDistance ) return true; return false; 2018 Question 1 Part A

2018 Question 1 Part B public double runSimulations( int num ) { double pos = 0; for( int i = 0; i < num; i++ ) if( simulate() ) pos++; } return pos / num; 2018 Question 1 Part B

Free Response Question 2 ArrayList © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com ArrayList A typical ArrayList question involves putting something into an ArrayList and removing something from an ArrayList. 34 76 -8 44 22 -998 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com ArrayList Arraylist is a class that houses an array. An ArrayList can store any type. All ArrayLists store the first reference at spot / index position 0. ArrayList can store a reference to any type of Object. ArrayList was built using an array[] of object references. 34 76 -8 44 22 -998 © A+ Computer Science - www.apluscompsci.com

frequently used methods © A+ Computer Science - www.apluscompsci.com ArrayList frequently 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; © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com ArrayList 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)); OUTPUT h c In the example above, ray is an ArrayList that stores String references. Casting would not be required to call non-Object methods on ray. ray.add(0,"hello"); ray.add(1,"chicken"); out.println(ray.get(0).charAt(0)); out.println(ray.get(1).charAt(5)); ray stores String references. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com ArrayList int spot=list.size()-1; while(spot>=0) { if(list.get(spot).equals("killIt")) list.remove(spot); spot--; } © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com ArrayList for(int spot=list.size()-1; i>=0; i--) { if(list.get(spot).equals("killIt")) list.remove(spot); } © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com ArrayList int spot=0; while(spot<list.size()) { if(list.get(spot).equals("killIt")) list.remove(spot); else spot++; } © A+ Computer Science - www.apluscompsci.com

2018 Question 2 Part A public WordPairList(String[] words) { allPairs = new ArrayList<WordPair>(); for( int i = 0; i < words.length; i++ ) for( int j = i + 1; j < words.length; j++ ) allPairs.add( new WordPair( words[i], words[j] ) ); } 2018 Question 2 Part A

2018 Question 2 Part B public int numMatches() { int count = 0; for( WordPair item : allPairs ) if(item.getFirst().equals(item.getSecond())) count++; } return count; 2018 Question 2 Part B

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Free Response Question 3 Implement an Interface Make a class © A+ Computer Science - www.apluscompsci.com © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Make a Class public Triangle(int a, int b, int c) { sideA=a; sideB=b; sideC=c; } Constructors are similar to methods. Constructors set the properties of an object to an initial state. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Make a Class public void setSideA(int a ) { sideA=a; } Modifier methods are methods that change the properties of an object. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Make a Class public int getSideA() { return sideA; } Accessor methods are methods that retrieve or grant access to the properties of an object, but do not make any changes. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Make a Class public class Triangle { private int sideA; private int sideB; private int sideC; Instance variables store the state information for an object. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Abstract / Interfaces public interface Exampleable { int writeIt(Object o); int x = 123; } All methods listed in an interface are public abstract. Abstract methods have no code. Each abstract method listed in an interface must be implemented in the class that implements the interface. All variables listed in an interface are public static final, making them final class variables. Interfaces cannot contain implemented methods, constructors, or instance variables. Methods are public abstract! Variables are public static final! © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Abstract / Interfaces public interface Exampleable { public abstract int writeIt(Object o); public static final int x = 123; } All methods listed in an interface are public abstract. Abstract methods have no code. Each abstract method listed in an interface must be implemented in the class that implements the interface. All variables listed in an interface are public static final, making them final class variables. Interfaces cannot contain implemented methods, constructors, or instance variables. Methods are public abstract! Variables are public static final! © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Abstract / Interfaces An interface is a list of abstract methods that must be implemented. An interface may not contain any implemented methods. Interfaces cannot have constructors!!! All methods listed in an interface are public abstract. Abstract methods have no code. Each abstract method listed in an interface must be implemented in the class that implements the interface. All variables listed in an interface are public static final, making them final class variables. Interfaces cannot contain implemented methods, constructors, or instance variables. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Abstract / Interfaces Interfaces are typically used when you know what you want an Object to do, but do not know how it will be done. If only the behavior is known, use an interface. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com String Love String s = "compsci"; 0 1 2 3 4 5 6 s c o m p s i A String is a group of characters. Strings are used to store words, which can consist of letters, numbers, and symbols. A string is a group of characters. The first character in the group is at spot 0. © A+ Computer Science - www.apluscompsci.com

frequently used methods © A+ Computer Science - www.apluscompsci.com String frequently 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 String is an immutable Object. String cannot be changed. All of the String methods are accessor method. All of the String methods are return methods. © A+ Computer Science - www.apluscompsci.com

frequently used methods © A+ Computer Science - www.apluscompsci.com String frequently used methods Name Use equals(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 The chart above lists some very common and very useful String class methods. equals() and compareTo() are used quite often. trim() and replaceAll() are very useful, but that widely used. toUpperCase() and toLowerCase() can be very useful in certain situations. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com String Love OUTPUT 4 -1 iga tors rule String sent = "alligators rule"; String find = "gato"; System.out.println( sent.indexOf( find ) ); System.out.println( sent.indexOf( "dog" ) ); System.out.println( sent.substring( 3 , 6 ) ); System.out.println( sent.substring( 6 ) ); © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com public class CodeWordChecker implements StringChecker { private int min; private int max; private String not; public CodeWordChecker( int a, int b, String c ) min = a; max = b; not = c; } public CodeWordChecker( String c ) min = 6; max = 20; public boolean isValid( String str ) if( str.indexOf( not ) > -1 ) return false; if( str.length() < min ) if( str.length() > max ) return true; public String toString() return "" + min + " " + max + " " + not; Make a Class 2017 Question 3 © A+ Computer Science - www.apluscompsci.com

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Free Response Question 4 Matrix © A+ Computer Science - www.apluscompsci.com © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices Typically, 1 question on the A test free response will require that students manipulate a 2-dimensional array. 0 1 2 0 1 2 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices A matrix is an array of arrays. int[][] mat = new int[3][3]; 0 1 2 0 1 2 Each spot in an matrix stores the location/address of an array. mat[0] stores the location / address of a one-dimensional array. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices A matrix is an array of arrays. int[][] mat = new int[3][3]; mat[0][1]=2; 0 1 2 2 0 1 2 Which array? Each spot in an matrix stores the location/address of an array. mat[0] stores the location / address of a one-dimensional array. mat[0][1]=2; This line sets mat[0] spot 1 to 2. Which spot? © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices 0 1 2 3 4 0 1 2 3 4 mat[2][2]=7; mat[0][3]=5; mat[4][1]=3 5 7 3 mat[2] stores the location / address of a one-dimensional array. mat[2][2]=7; This line sets mat[2] spot 2 to 7. © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices for( int r = 0; r < mat.length; r++) { for( int c = 0; c < mat[r].length; c++) mat[r][c] = r*c; } 1 2 4 if mat was 3x3 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices A matrix is an array of arrays. int[][] mat = new int[3][3]; 0 1 2 # of arrays size of each array 0 1 2 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices – for each 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(); The for each loop works quite well as tool to print a matrix. OUTPUT 5 7 5 3 4 6 0 8 9 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Matrices – for loop int[][] mat = {{5,7},{5,3,4,6},{0,8,9}}; for( int r = 0; r < mat.length; r++ ) { for( int c = 0; c < mat[r].length; c++ ) System.out.print( mat[r][c] + " "); } System.out.println(); The for each loop works quite well as tool to print a matrix. OUTPUT 5 7 5 3 4 6 0 8 9 © A+ Computer Science - www.apluscompsci.com

public static int[] getColumn( int[][] arr2D, int c ) { int[] col = new int[arr2D.length]; for( int r = 0; r < arr2D.length; r++ ) col[r] = arr2D[r][c]; } return col; 2018 Question 4 part A

public static boolean isLatin( int[][] square ) { if( containsDuplicates( square[0] ) ) return false; for( int i = 1; i < square.length; i++ ) if( ! hasAllValues( square[0], square[i] ) ) } for( int i = 0; i<square[0].length; i++) if( ! hasAllValues( square[0] , getColumn( square, i) ) ) return true; 2018 Question 4 part B.1

public static boolean isLatin( int[][] square ) { if( containsDuplicates( square[0] ) ) return false; for( int i = 1; i < square.length; i++ ) if( ! hasAllValues( square[0], square[i] ) ) if( ! hasAllValues( square[0] , getColumn( square, i) ) ) } return true; 2018 Question 4 part B.2 Probably not the most common solution.

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© A+ Computer Science - www.apluscompsci.com Multiple Choice -answer the easiest question 1st -work through the test more than once -use the test to take the test -work more time intensive problems last -bubble answers on answer sheet as you go -answer every question -keep track of your time - 90 minutes © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 – 90 minutes © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 -return from all return methods -return correct data type from return methods © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -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 -check for public/private on methods/variables -make super calls in sub class methods as needed © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response -When extending abstract / implementing interface -know which methods the parent contains -have the original class where you can see it -make sure you have super calls -check for public/private on methods/variables -make super calls in sub class methods as needed -implement all abstract methods in sub class © A+ Computer Science - www.apluscompsci.com

© A+ Computer Science - www.apluscompsci.com Free Response Topics Algorithms – ifs and loops ArrayList – get,set,remove,add,size Make a Class – Implement an Interface – create a class that implements an interface Arrays and Matrices – nested loops - array of arrays concepts © A+ Computer Science - www.apluscompsci.com

A+ Computer Science AP Review 2018 AP CS A EXAM