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131 Lab slides (all in one)

  1. Nov 17. Lab17 Recap the quiz http://www.slideshare.net/takyeon
  2. String Immutable Every time you alter String values, it will allocate another exact amount of space in the heap. The previous value in the memory will be garbage-collected later. Mutable When created it reserves a certain amount of space in the heap, which can be larger than the value. Within that space, values can be modified without additional memory use. When the value requires more space, the space will automatically grow larger. StringBuffer String s = "a"; s += "b"; s += "c"; ab abc a s StringBuffer s = new StringBuffer("a"); s.append("b"); s.append("c"); a s … buffer size: 1+16 b c
  3. array 0 0 0 CAUGHT FINAL PROG END
  4. public static int[] buildN(int n) { int[] arr = new int[n]; for(int i=0;i<n;i++) { arr[i] = i+1; } return arr; }
  5. public class BreakAndContinue { public static void main(String[] args) { int i; System.out.println("Example 1"); for (i = 1; i <= 5; i++) { System.out.print(i); if (i == 3) { break; } System.out.println(" " + i); } System.out.println("nThe value of i after the loop is: " + i); System.out.println("nExample 2"); for (i = 1; i <= 5; i++) { System.out.print(i); if (i == 3) { continue; } System.out.println(" " + i); } System.out.println("nThe value of i after the loop is: " + i); } } We will jump out in the middle of a for loop meant for 5 iterations We will skip over part of iteration #3 break and continue
  6. packages A package is a grouping of related types (classes, interfaces, enumerations, and annotation).
  7. packages /* File name : Animal.java */ package animals; public class Mammals { public void eat(); public void travel(); } - Create a package at the top of the source code. - lowercase. /* File name : oneDriver.java */ … animals.Mammals m1 = new animals.Mammals(); … /* File name : anotherDriver.java */ import animals.*; Mammals m1 = new Mammals(); … - After import, we can call any public classes inside the animals package without full path. - In other packages, without import, you need to specify full package path Using it Creating package
  8. import java.util.Date; import my.own.Date; class Test{ public static void main(String [] args){ // how can I use both Date types??? namespace conflict! } } packages class Test{ public static void main(String [] args){ my.own.Date myDate = new my.own.Date(); java.util.Date javaDate = new java.util.Date(); } } Instead of importing both, use full-path to the type
  9. /* Animal.java */ package interfaceExample; public interface Animal { public String getName(); public void setName(String s); public String makeSound(); public String toString(); } /* Cat.java */ package interfaceExample; public class Cat implements Animal { private String animalName; public Cat(String nameIn) { animalName = nameIn; } public String getName() { return animalName; } public void setName(String nameIn) { animalName = nameIn; } public String makeSound() { return "meow"; } public String toString() { return animalName; } … /* Dog.java */ package interfaceExample; public class Dog implements Animal { private int burriedBonesCount; private String animalName; public Dog(String nameIn) { animalName = nameIn; burriedBonesCount = 0; } public … interfaceExample Animal Cat Dog interface Cat and Dog classes must have every method defined in the Animal interface.
  10. package interfaceExample; public class PetDriver { public static void main(String [] args) { Animal[] pets = new Animal[3]; pets[0] = new Cat("Neko"); pets[1] = new Dog("Fluffy"); pets[2] = new Cat("Crookshanks"); Animal temp; for (int i=0; i<pets.length; i++) { temp = pets[i]; System.out.println(temp.getName() + " says " + temp.makeSound()); } } } interfaceExample Animal Cat Dog
  11. Nov 10. Lab16 Recap the quiz http://www.slideshare.net/takyeon
  12. When can we access private fields? 1) In the same class or 2) when the object is passed as a parameter. Question. Can we access private fields of an object in JUnit test?
  13. ! No button in debugger makes the program "skip" code. ! They all run the following code, but pause at different positions. [step over] "run the current line, and pause at the next line." [step into] "go into the first method that will be invoked in the current line, and pause at the first line of the method. If there's no method to go into, then pause at the next line." [step return] "run the following lines of code, and pause after returning." public int met() { long startTime = new Date().getTime(); System.out.print("Current Time: "+startTime.toString()); for (int i = 0; i < 50000; i++) { startTime++; } return startTime; } step into will go into java.lang.Long.toString() method. step over will run the current line and pause at the next line. step return will run the remaining lines and pause after returning.
  14. Rational r = new Rational(8,3); assertEquals(r.getNumer(), 8); assertEquals(r.getDenom(), 3);assertEquals is a static method of jnit.assert class numer and denom are private fields. You cannot access them with r.numer or r.demon
  15. assertEquals(r.getNumer(), 8); assertEquals(r.getDenom(), 3); assertTrue(r.getNumer() == 8 && r.getDenom() == 3); if(r.getNumer()==8 && r.getDenom() == 3) { assertTrue(true); } else { assertFalse(false); } Are these all same? Then which one is the best practice? Different codes, same test Compact, but cannot tell which one failed. Unnecessarily complicated code.
  16. private int currFloor; public Elevator(int currFloorIn) { if(floorNum<1) { currFloor = 1; } else if(floorNum>5) { currFloor = 5; } else { currFloor=floorNum; } } public void setCurrFloor(int floorNum) { if(floorNum<1) { currFloor = 1; } else if(floorNum>5) { currFloor = 5; } else { currFloor=floorNum; } } public int getCurrFloor() { return currFloor; }
  17. STACK HEAP valA 8 21 valc valB 20 This is because valA, valB, valC are Integer objects not primitive data type int.
  18. Card deck exercise 1. Make a group of four people (with at least one card deck) 2. Shuffle the deck 3. Deal out 5 cards to each, and discuss which wacky hands each have. 4. Deal out two cards to each and three as community cards. Discuss who got the best hand.
  19. Nov 5. Lab15. Exceptions http://www.slideshare.net/takyeon
  20. CVS / Lab08 public static int[] tallyArray(int[] arrayIn) throws RuntimeException { int[] retArr = new int[10]; //Your code goes here… } It will return an int array. It will accept an int array. input array output array # of occurrances of the value i+1 exception [1,10,1,9,9] [2,0,0,0,0,0,0,0,2,1] [1,2,3] [1,1,1,0,0,0,0,0,0,0] [10] [0,0,0,0,0,0,0,0,0,1] null [0,0,0,0,0,0,0,0,0,0] [1,10,1,9,11] RuntimeException: "Ooops. Sorry about that" [1,10,1,9,0] RuntimeException: "Ooops. Sorry about that"
  21. Use exceptions instead of if-conditionals for(int i=0;i<arrayIn.length;i++) { retArr[arrayIn[i]-1]++; } Basic code without handling exceptional cases There are two exceptions can be thrown. 1. when arrayIn is null NullPointerException will be thrown  should return [0,0,0,0,0,0,0,0,0,0] 2. when arrayIn contains a number <1 or >10 ArrayIndexOutOfBoundsException will be thrown  should throw RuntimeException: "Ooops. Sorry about that." Catch and handle these exceptions individually. DO NOT USE IF-CONDITIONALS
  22. RuntimeException e = new RuntimeException("ahaha"); throw e; // same thing throw new RuntimeException("Ooops.");
  23. Nov 3. Lab14. Ternary operator (a>b ? a:b) Switch http://www.slideshare.net/takyeon
  24. Disclaimer Everything I told in the lab sessions that are not taught in lectures are optional.
  25. Ternary operator if (a>b) { result = "ha"; else { result = "ho"; } result = a > b ? "ha" : "ho"; = If condition is true, then the expression is evaluated to value_if_true, otherwise it will be value_if_false. condition ? value_if_true : value_if_false Practice. Write a method that accepts an int parameter "numCookies" and prints out (if numCookies is 1) "There is 1 cookie in the jar." (if numCookies is n) "There are n cookies in the jar." * Do not use if-else. Use ternary operator. * Assume numCookies is a positive number (>0).
  26. Switch Simpler and more readible version of if-then-else statements int month = 8; String monthString; switch (month) { case 1: monthString = "January"; break; case 2: monthString = "February"; break; … default: monthString = "Invalid month"; break; } int month = 8; String monthString; if (month == 1) { monthString = "January"; } else if (month == 2) { monthString = "February"; } else if (month == 3) { … } else { monthString = "Invalid month"; } ... // and so on = Why should I break? "default" is like "else"
  27. Practice. Write a method that accepts a char parameter, which will be an uppercase letter, and then uses a switch statement to return an int based on the number of "pen strokes" to draw the letter. If the parameter is not an uppercase letter, return -1. e.g. If 'C' is given, then it should return 1. e.g. If 'D' is given, then it should return 2. Characters with 1 stroke : C,L,M,N,O,S,U,V,W,Z Characters with 2 strokes : D,G,J,P,Q,T,X Characters with 3 strokes : A,B,F,H,I,K,R,Y Characters with 4 strokes : E * Do not use if-else. Use switch * You can combine multiple cases in a single line like below case 'C': case 'L': case 'M' … Switch
  28. Oct 29th Lab13. Mutability Exception handling Unit test http://www.slideshare.net/takyeon
  29. Further readings on "Why String is immutable in Java?" http://www.programcreek.com/2013/04/why-string-is-immutable-in-java/ Mutable objects Immutable objects Contains setter methods e.g. photo.setPixel(row,col,pixel) No setter methods e.g. pixel object had no setRed(value) Not all data fields are final All data fields are final StringBuffer, MutableInt, Photo class in Project 3 String, Integer, Pixel class in Project 3 (+) Fast when updating data fields (-) Must use deep copy (-) 1000 times slower than mutable ojb (+) Shallow copy is okay (+) Create once and use multiple times e.g. You could use one black pixel to paint weirdCombination's background in black.
  30. Deep copy Shallow copy (+) Changing Peggy(b1)'s information will not affect Peggy(b2) (+) Changing Peggy(b1)'s information will affect Peggy(b2) public Bag(Bag other) { this.p1 = other.p1; this.p2 = other.p2; this.p3 = other.p3; this.p4 = other.p4; } Bag b2 = new Bag(b1); public Bag(Bag other) { this.p1 = new Person(other.p1); this.p2 = new Person(other.p21); this.p3 = new Person(other.p3); this.p4 = new Person(other.p4); } Bag b2 = new Bag(b1); Shallow copy is safe if Person objects are immutable. Deep copy is safe if Person objects are mutable.
  31. … public Rational(int numberIn, int denomIn) { if (denomIn==0) throw new ArithmeticException("Divide by Zero"); numer = numerIn; denom = denomIn; } … public Rational divide(Rational other) { try { return multiply(this, other.reciprocal()); } catch(ArithmeticException e) { System.out.println("An exception caught at divide."); } } … public Rational reciprocal() { return new Rational(denom, number); } … Exceptions // in testDivide() method Rational r2 = new Rational(5,11); Rational s2 = new Rational(0, 9); try { r2.divide(s2); assertTrue(false); } catch (ArithmeticException e) { assertTrue(true); } testDivide() divide() reciprocal multiply Constructor throw Do not catch Catch and print out "An exception caught at divide." Nothing to catch. Will fail the test.
  32. How to design unit test public void testDivide() { Rational r1 = new Rational(7,11); Rational s1 = new Rational(5, 3); Rational p1 = r1.divide(s1); assertEquals(21, p1.getNumer()); assertEquals(55, p1.getDenom()); Rational r2 = new Rational(5,11); Rational s2 = new Rational(0, 9); try { r2.divide(s2); assertTrue(false); } catch (ArithmeticException e) { assertTrue(true); } } Test a common use case. Test an exceptional case. 1. Manual test If ArithmeticException is thrown by divde method, it will pass the test. This line will throw an exception If executed, this line will always fail the test.
  33. 2. Using an oracle How to design unit test public void add() { Random rnd = new Random(7); Rational rationalValueA; Rational rationalValueB; Rational rationalAnswer; int v1, v2, v3, v4; for (int i=0; i<1000; i++) { v1 = rnd.nextInt(500); v2 = rnd.nextInt(500); v3 = rnd.nextInt(500); v4 = rnd.nextInt(500); rationalValueA = new Rational(v1, v2); rationalValueB = new Rational(v3, v4); rationalAnswer = rationalValueA.add(rationalValueB); assertEquals("Trying " + rationalValueA + " plus " + rationalValueB, v1*v4 + v2*v3, rationalAnswer.getNumer()); assertEquals("Trying " + rationalValueA + " plus " + rationalValueB, v2 * v4, rationalAnswer.getDenom()); } } This is how the add method is supposed to work. Repeat 1000 times with random settings.
  34. Oct 27th Lab12. String methods Debugging http://www.slideshare.net/takyeon
  35. String methods String str = "studytonight"; System.out.println(str.charAt(2)); // => u charAt(int i) returns the character at the index i position String a = "a"; String b = "b"; System.out.println(a.compareTo(b)); // => -1 System.out.println(b.compareTo(a)); // => 1 System.out.println(a.compareTo(a)); // => 0 a.compareTo(b) compares a and b lexicographically.
  36. String methods String str = "The quick brown fox jumps over the lazy dog"; System.out.println(str.indexOf('u')); // => 5 System.out.println(str.indexOf('&')); // => -1 System.out.println(str.indexOf(' ')); // => 3 System.out.println(str.indexOf(' ',3)); // => 3 System.out.println(str.indexOf(' ',4)); // => 9 a.indexOf(int ch) returns the first index of ch within a a.indexOf(String s) returns the first index of s within a a.indexOf(int ch, int fromIndex) returns the first index of ch within a, starting search at the fromIndex
  37. String methods String str = "1-2-3-4-5"; System.out.println(str.replace('-',' ')); // => "1 2 3 4 5" a.replace(char oldCh, char newCh) returns a new string resulting from replacing all oldCh in a with newCh String str = "aaaaa"; System.out.println(str.replace('a','b')); //=> "bbbbb" System.out.println(str.replace("aa","b")); //=> "bba" System.out.println(str.replace("aaa","a")); //=> "aaa" a.replace(CharSequence o, CharSequence n) returns a new string resulting from replacing all o in a with n Can be CharBuffer, Segment, String, StringBuffer, StringBuilder Newly added string will not be evaluated.
  38. String methods String str = "0-2-4-6-8"; System.out.println(str.substring(4)); // => "4-6-8" a.substring(int beginIndex) returns a new string from beginIndex till the end String str = "0-2-4-6-8"; System.out.println(str.substring(4,8)); // => "4-6-" a.substring(int beginIndex, int endIndex) returns a new string from beginIndex (inclusive) till endIndex (exclusive)
  39. http://codingbat.com/java
  40. Debugging Trace program's behavior line-by-line Step 1. Set "break point" at the suspicious line Step 2. Run the debugger next line into Step 3. - Examine the contents of memory - Decide how to proceed with running/debugging the program by either stepping "over", "into", or "out of" code segments out of
  41. Debugging Conditional breakpoint
  42. Oct 20th Lab11. Mid-term #1 review Javadoc http://www.slideshare.net/takyeon
  43. Midterm review Regrading request - Write it on a separate sheet of paper - Hand it in to professor with your exam. - The entire exam will be regraded.
  44. - Will our culture really be defined by interfaces? - What "uses" are there for information visualization in terms of explaining things to the general public. - Mechanical Turk * ethics (pay is below US minimum wage) * what would they want to do using Mechanical Turk * origins of the name (interesting con around a chess playing machine around 200 years ago) - Art and Computer Science * can CS people create art? can Art people create CS? * what ideas do they have in terms of CS changing the Art world * ask if any of them have been to the 3rd floor of CSIC and seen the Treemap art gallery
  45. Javadoc: Java Documentation Comments Javadoc is a tool which comes with JDK and it is used for generating Java code documentation in HTML format from Java source code which has required documentation in a predefined format. source code generated documentation web page block comment that starts with /** @tagName to add special tags
  46. Javadoc: Java Documentation Comments @param Adds a parameter with the specified parameter-name followed by the specified description to the "Parameters" section. @return Adds a "Returns" section with the description text. @return description @see Adds a "See Also" heading with a link or text entry that points to reference. @throws Adds a Throws subheading to the generated documentation, with the class- name and description text..
  47. Oct 13th Lab09. Stack, Heap, and Metaspace http://www.slideshare.net/takyeon
  48. public class Student { public String name; public int tokenLevel; private static int currentCount = 0; private static final int DEFAULT_TOKENS = 3; public Student() { name = "unknown"; tokenLevel = DEFAULT_TOKENS; currentCount++; } } Student s1 = new Student(); s1.name = "Tak"; STACK HEAP META SPACE DEFAULT_TOKENS 0 3 currentCount 1 X s1 name tokenLevel 3 "unknown" "Tak" constructor All static fields of a class live in Metaspace. All local variables (both primitives and references) live on the stack. Non- primitive data objects are stored in the heap, and referenced by variables on the stack. All non-primitive objects live on the heap. Primitive instance variables of those objects are stored inside the object. Non-primitive variables are stored outside of the object, and referenced by the instance variable.
  49. Size? 5 * *** ***** ******* ********* Scanner sc = new Scanner(System.in); int size = sc.nextInt(); for(int row=0; row<size; row++) { for(int col=0;col<4-row;col++) { System.out.print(" "); } for(int col=0;col<row*2+1;col++) { System.out.print("*"); } System.out.println(); } sc.close(); row col : 1st spaces before * col : 2nd number of * 0 4 1 1 3 3 2 2 5 3 1 7 4 0 9
  50. int x,y; x=2; y=5; System.out.println(x++ * y++); System.out.println(++x * ++y); System.out.println(++x * y++); System.out.println(x++ * ++y); System.out.println("1 + 2 = " + 1 + 2); System.out.println("1 + 2 = " + (1 + 2)); 1 + 2 = 12 1 + 2 = 3 year % 4 == 0 && year % 100 != 0 || year % 400 == 0 ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)
  51. Any question?
  52. Oct 8th Lab08. Quiz review Triangle and Stripes http://www.slideshare.net/takyeon
  53. Quiz review No i++ ++i Use and then increase int i = 3; int a = i++; // a = 3, i = 4 int b = ++a; // b = 4, a = 4 Increase and then use
  54. Quiz review maxCount 100 str "Hello" "HELLO" • Whenever a new variable is declared, it is added to STACK. • Primitive data types are stored in STACK • byte, short, int, long, float, double, boolean, char • Other data types are stored in HEAP. • String, Integer, Scanner, … • Data in HEAP are not immediately deleted but unlinked, and will be garbage-collected.
  55. public static void main(String[] args) { Scanner sc = new Scanner(System.in); int size = sc.nextInt(); for(int row=1;row<=size;row++) { for(int col=1;col<=size;col++) { System.out.print(row*col + " "); } System.out.println(); } }
  56. Lab – 2D drawing Two methods. 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 4,0 4,1 4,2 4,3 4,4 M1. Iterate pixels to paint for (int i=0; i<size; i++) { grid.setColor(i, i, Color.BLUE); } Intuitive and efficient  M2. Iterate every pixel, use if conditionals to check pixels to paint for (int row=0; row<size; row++) { for (int col=0; col<size; col++) { if(row==col) { grid.setColor(row, col, Color.BLUE); } } } Complex and inefficient  BUT! More generalizable
  57. Lab – 2D drawing Two methods. 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 4,0 4,1 4,2 4,3 4,4 M2. Iterate every pixel, use if conditionals to check pixels to paint for (int row=0; row<size; row++) { for (int col=0; col<size; col++) { if(row!=col) { grid.setColor(row, col, Color.BLUE); } } } You can simply inverse the conditional logic M1. Iterate pixels to paint Very difficult  Now you want to paint all the pixels except the diagonal line.
  58. 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 4,0 4,1 4,2 4,3 4,4 More examples. row>2 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 4,0 4,1 4,2 4,3 4,4 row%2 == 1 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 4,0 4,1 4,2 4,3 4,4 col%2 == 1 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 4,0 4,1 4,2 4,3 4,4 (row-col)>=0 0 -1 -2 -3 -4 1 0 -1 -2 -3 2 1 0 -1 -2 3 2 1 0 -1 4 3 2 1 0 row-col Diagonal shapes require both row and col Linear shapes require either row or col.
  59. Transformation > Move 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 4,0 4,1 4,2 4,3 4,4 (row+1, col) (row+1)-col >= 0 -1 -2 -3 -4 -5 0 -1 -2 -3 -4 1 0 -1 -2 -3 2 1 0 -1 -2 3 2 1 0 -1 (row+1)-col 0,1 0,2 0,3 0,4 0,5 1,1 1,2 1,3 1,4 1,5 2,1 2,2 2,3 2,4 2,5 3,1 3,2 3,3 3,4 3,5 4,1 4,2 4,3 4,4 4,5 To move a shape to left by 1 pixel, replace "row" with "row+1"
  60. Transformation > Horizontal Flip. 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 4,0 4,1 4,2 4,3 4,4 0,4 0,3 0,2 0,1 0,0 1,4 1,3 1,2 1,1 1,0 2,4 2,3 2,2 2,1 2,0 3,4 3,3 3,2 3,1 3,0 4,4 4,3 4,2 4,1 4,0 Horizontal Flip (row, 4-col) (row-(4-col))>=0 -4 -3 -2 -1 0 -3 -2 -1 0 1 -2 -1 0 1 2 -1 0 1 2 3 0 1 2 3 4 row-(4-col) To flip a shape, multiple row or column by -1, and add size -col size-col col col 4 := size of the shape – 1 Why -1? Because our row and col index started from 0.
  61. 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 4,0 4,1 4,2 4,3 4,4 Vertical Flip (4-row, col) (4-row)-col >= 0 4 3 2 1 0 3 2 1 0 -1 2 1 0 -1 -2 1 0 -1 -2 -3 0 -1 -2 -3 -4 (4-row)-col 4,0 4,1 4,2 4,3 4,4 3,0 3,1 3,2 3,3 3,4 2,0 2,1 2,2 2,3 2,4 1,0 1,1 1,2 1,3 1,4 0,0 0,1 0,2 0,3 0,4 Transformation > Vertical Flip.
  62. (row-col)>=0 0 -1 -2 -3 -4 1 0 -1 -2 -3 2 1 0 -1 -2 3 2 1 0 -1 4 3 2 1 0 (row-(4-col))>=0 -4 -3 -2 -1 0 -3 -2 -1 0 1 -2 -1 0 1 2 -1 0 1 2 3 0 1 2 3 4 Horizontal Flip (4-row)-col >= 0 4 3 2 1 0 3 2 1 0 -1 2 1 0 -1 -2 1 0 -1 -2 -3 0 -1 -2 -3 -4 Vertical flip (4-row)-(4-col) >= 0 0 1 2 3 4 -1 0 1 2 3 -2 -1 0 1 2 -3 -2 -1 0 1 -4 -3 -2 -1 0 Horizontal Flip col-row >= 0 Vertical flip
  63. Oct 6th Lab07. Loop applications
  64. public void commonFactor(int n1, int n2) { for(int i=1; i<=min(n1,n2); i++) { if(n1%i==0 && n2%i==0) { System.out.println(i); } } } Finding common factors of two numbers Common factors can divide both numbers. E.g. Common factors of 9 and 12  1 and 3 Common factors of 24 and 78  1, 2, 3, and 6
  65. compareTo method String s1 = "aaa"; String s2 = "aac"; int k = s1.compareTo(s2); // k => -2 Compares s1 and s2 lexicographically. Negative if s1 precedes s2 Positive if s1 follows s2 Zero if s1 is equal to s2
  66. Get multiple words, find the first and the last words 1) Using while loop, keep asking words until "STOP" 2) Using compareTo, update the first and the last words 3) Print out
  67. Oct 1st Lab06. 2D drawing
  68. SquareGrid.java ExampleDriver.java • Prompt a shape question • Create an empty grid • Draw the requested shape OperatorMaker.java drawOp (SquareGrid grid, int symbol) minus, plus, divide, multiply (SquareGrid grid) You will change only these methods  Drawing shapes on 2D grid
  69. Single loop for drawing a line 1) How can we get the middle row number?0 size : 7 3 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 4,0 4,1 4,2 4,3 4,4 int size = grid.getHt(); int midRow = size / 2; 2) How to draw a line? • Iterate over columns (0 – 4) • Paint the middle cell for (int iCol=0; iCol<size; iCol++) { grid.setColor(midRow, iCol, Color.BLUE); }
  70. Single loop for drawing a line 1) How can we get the middle column number?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 4,0 4,1 4,2 4,3 4,4 int size = grid.getWd(); int midCol = size / 2; 2) How to draw a line? • Iterate over rows (0 – 4) • Paint the middle cell for (int iRow=0; iRow<size; iRow++) { grid.setColor(iRow, midCol, Color.BLUE); } Notice that drawing horizontal and vertical lines are quite similar. We just switched row and column variables.
  71. Single loop for drawing a line 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 4,0 4,1 4,2 4,3 4,4 1) How to draw a line? • Iterate over rows or columns (0-4) • Paint diagonal cells. for (int iRow=0; iRow<size; iRow++) { grid.setColor(iRow, iRow, Color.BLUE); }
  72. for (int iCol=0; iCol<size; iCol++) { grid.setColor(midRow, iCol, Color.BLUE); } for (int iRow=0; iRow<size; iRow++) { grid.setColor(iRow, midCol, Color.BLUE); } for (int iRow=0; iRow<size; iRow++) { grid.setColor(iRow, iRow, Color.BLUE); } 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 4,0 4,1 4,2 4,3 4,4 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 4,0 4,1 4,2 4,3 4,4 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 4,0 4,1 4,2 4,3 4,4 for (int iCol=0; iCol<size; iCol++) { grid.setColor(iCol, iCol, Color.BLUE); } or
  73. Single loop for drawing a line Iterating over the columns, paint the middle cell. Iterating over the columns, paint the middle cell. Iterating over the rows, paint the center cell. Iterating over the columns, paint i-th cell. Draw Plus, Divide, and Divide (rotated).
  74. Sep 29th Lab05. 1. Recap the quiz #1 2. String Class 3. static vs. instance method
  75. Recap quiz #1. PRINT your names in the grade server. NO nicknames.
  76. Recap quiz #1. Use specific technical keywords e.g. What does CVS “do” for us? 1. Check out / Download the starter files 2. Store / Save multiple versions of the source code share, deliver, get, access, connected people, ... Penalties for inaccurate extra info e.g. CVS runs our code and give us grades.  -1 for incorrect extra info.
  77. String Class String s = “hello”; Create a new String object with an initial value “hello” String objects have many convenient methods, upperS = s.toUpperCase(); // will set upperS to “HELLO” whereIsl= s.indexOf(‘l’); // will find the position of the first ‘l’ newS = s.replace(‘e’,’a’); // will set newS to “hallo”
  78. int type vs. Integer Class int i=0; Primitive data type Integer i = 17; Wrapper Class don’t have much method provide methods - convert to string - generate hash codes Faster A little slower
  79. Static vs. Instance method Intance methods need a sheep as a subject. bob.eat(); bob.smileTo(clara); bob.getPenNumber(); Static methods are about all the sheeps. Sheep.getTotalSheep(); Sheep.removeAll(); Sheep.addSheep(‘evan’);
  80. Sep 24th Lab04. Loop
  81. Flow of Control 1. Top-to-bottom statements 2. Method calls 3. Conditional statements 4. Iteration (loop) for, while, ...
  82. Two goals of iteration 1. Automation Reduce repetition of code System.out.println(“****”); System.out.println(“****”); System.out.println(“****”); How can we reduce? for(int i=0;i<3;i++) { System.out.println(“****”); } 2. Abstraction Code for various situations System.out.println(“****”); How can we print n-number of “*”?
  83. From manual & concrete to automatic & abstract Level 1. Draw 30 by 10 rectangle (hard-coded) System.out.println(“**********”); System.out.println(“**********”); System.out.println(“**********”); ... 27 more lines Level 2. Draw 30 by 10 rectangle (single-loop)  Too many copy & paste. Hard to modify. int row=0; while(row<30) { System.out.println(“**********”); row++; }  A little more compact.  Still too many * for each line.
  84. From manual & concrete to automatic & abstract Level 3. Draw 30 by 10 rectangle (nested-loop) int row=0, col=0; while(row<30) { while(col<10) { System.out.print(“*”); } System.out.println(); }  Much compact.  Cannot change # of row and col Level 4. Draw height by width (nested-loop, parameterized) int row=0, col=0; int height=30, width=10; while(row<height) { while(col<width) { System.out.print(“*”); } System.out.println(); }  Compact  Can draw any sized rectangle
  85. iterartor line 1 0 value line 2 0 target line 4
  86. answer line 1 1 i line 1 1 j line 1 0
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