CIS November 14, 2017

Transcription

1 CIS 1068 November 14, 2017

2 Administrative Stuff Netflix Challenge New assignment posted soon Lab grades

3 Last Time. Building Our Own Classes Why Abstraction More on the new operator Fields Class vs the user of the class (aka client)

4 public class WhatsPrinted2 { public static void main(string args[]) { String s1=""; for (int i=0; i<2; i++) { String s2 = "baa"; for (int j=0; j<2; j++) { if ((i+j)%2==0) { s1+="a"; } else { s2+=s2; } } } System.out.println(s2); } }

5 public class WhatsPrinted2 { public static void main(string args[]) { String s1=""; for (int i=0; i<2; i++) { String s2 = "baa"; for (int j=0; j<2; j++) { if ((i+j)%2==0) { s1+="a"; } else { s2+=s2; } } } System.out.println(s2); } } Answer s2 is out of scope. Error

6 How much is a megabyte?

7 How much is a megabyte? about a million or 220

8 1 public class Mystery11 { 2 public static void func(int x, int y, int z) { 3 if (x>y+z) { 4 x+=y; 5 } 6 y--; 7 z=z%2; 8 } 9 public static void main(string args[]) { 10 int x=10, y=20, z=30; 11 func(z, x, y); 12 System.out.println(x); 13 } 14 }

9 1 public class Mystery11 { 2 public static void func(int x, int y, int z) { 3 if (x>y+z) { 4 x+=y; 5 } 6 y--; 7 z=z%2; 8 } 9 public static void main(string args[]) { 10 int x=10, y=20, z=30; 11 func(z, x, y); 12 System.out.println(x); 13 } 14 } answer x is 10. func( ) operates on copies, not the originals

10 1 import java.util.arrays; 2 public class Mystery07 { 3 public static final int SIZE=10; 4 public static void update(int A[], int x) { 5 for (int i=0; i<a.length; i++) { 6 A[i]+=x; 7 } 8 } 9 10 public static void main(string args[]) { 11 int A[] = new int[size]; 12 for (int i=0; i<a.length; i++) { 13 A[i]=i*10; 14 } 15 update(a, 6); 16 System.out.println(A[1]); 17 } 18 }

11 1 import java.util.arrays; 2 public class Mystery07 { 3 public static final int SIZE=10; 4 public static void update(int A[], int x) { 5 for (int i=0; i<a.length; i++) { 6 A[i]+=x; 7 } 8 } 9 10 public static void main(string args[]) { 11 int A[] = new int[size]; 12 for (int i=0; i<a.length; i++) { 13 A[i]=i*10; 14 } 15 update(a, 6); 16 System.out.println(A[1]); 17 } 18 } Answer 16

12 1 public class Mystery12 { 2 public static void func(int x, int y, int z) { 3 if (x>y+z) { 4 x+=y; 5 } 6 y--; 7 z=z%2; 8 System.out.println(x); 9 } 10 public static void main(string args[]) { 11 int x=11, y=19, z=31; 12 func(z, x, y); 13 } 14 }

13 1 public class Mystery12 { 2 public static void func(int x, int y, int z) { 3 if (x>y+z) { 4 x+=y; 5 } 6 y--; 7 z=z%2; 8 System.out.println(x); 9 } 10 public static void main(string args[]) { 11 int x=11, y=19, z=31; 12 func(z, x, y); 13 } 14 } Answer 42

14 1 public class WhatsPrinted5 { 2 public static int func(int y) { 3 return y*2; 4 } 5 6 public static void main(string args[]) { 7 int x=10; 8 9 func(x); 10 System.out.println(x); 11 } 12 }

15 1 public class WhatsPrinted5 { 2 public static int func(int y) { 3 return y*2; 4 } 5 6 public static void main(string args[]) { 7 int x=10; 8 9 func(x); 10 System.out.println(x); 11 } 12 } Answer 10. Again, func( ) operates on copies, not the original. Return value not read.

16 1 public class WhatsPrinted3 { 2 public static void whatsprinted(int A[]) { 3 for (int i=1; i<a.length; i++) { 4 A[i]+=A[i-1]+1; 5 } 6 } 7 8 public static void main(string args[]) { 9 int A[] = {9,2,6,8,7}; 10 whatsprinted(a); 11 System.out.println(A[A.length-1]); 12 } 13 }

17 1 public class WhatsPrinted3 { 2 public static void whatsprinted(int A[]) { 3 for (int i=1; i<a.length; i++) { 4 A[i]+=A[i-1]+1; 5 } 6 } 7 8 public static void main(string args[]) { 9 int A[] = {9,2,6,8,7}; 10 whatsprinted(a); 11 System.out.println(A[A.length-1]); 12 } 13 } Answer 36

18 Suppose that we have A, which is a two-dimensional array of int. Which of the following gives us the item in A which is stored in the first row, last column? A[length-1][0] A[0][A[0].length-1] Impossible to tell with the information given. A[0][length-1] A[0].length-1

19 Suppose that we have A, which is a two-dimensional array of int. Which of the following gives us the item in A which is stored in the first row, last column? A[length-1][0] **** A[0][A[0].length-1] **** Impossible to tell with the information given. A[0][length-1] A[0].length-1

20 Which analogy is most accurate? cookie cutter is to cookie as object is to class cookie is to cookie cutter as object is to class cookie cutter is to cookie as blueprint is to object cookie is to cookie cutter as blueprint-class is to class cookie is to cookie cutter as base class is to object

21 Which analogy is most accurate? cookie cutter is to cookie as object is to class cookie is to cookie cutter as object is to class cookie cutter is to cookie as blueprint is to object cookie is to cookie cutter as blueprint-class is to class cookie is to cookie cutter as base class is to object

22 1 public class WhatsPrinted1 { 2 public static void main(string args[]) { 3 int x=0; 4 do { 5 System.out.print(x + " "); 6 x--; 7 } while (x>10); 8 System.out.println(); 9 } 10 }

23 1 public class WhatsPrinted1 { 2 public static void main(string args[]) { 3 int x=0; 4 do { 5 System.out.print(x + " "); 6 x--; 7 } while (x>10); 8 System.out.println(); 9 } 10 } Answer 0. With a do-while loop, we always do the body at least once.

24 1 public class MysteryShack { 2 public static int[] mystery(int A[]) { 3 int B[] = new int[a.length]; 4 5 for (int i=0; i<a.length; i++) { 6 B[i]=A[i]*10; 7 } 8 9 return B; 10 } 11 public static void main(string args[]) { 12 int A[]={100,200,300,400,500}; 13 int B[]={10,20,30,40,50}; 14 int C[]; C=mystery(B); 17 if (C==A) { 18 System.out.println("same"); 19 } else { 20 System.out.println("different"); 21 } 22 } 23 }

25 1 public class MysteryShack { 2 public static int[] mystery(int A[]) { 3 int B[] = new int[a.length]; 4 5 for (int i=0; i<a.length; i++) { 6 B[i]=A[i]*10; 7 } 8 9 return B; 10 } 11 public static void main(string args[]) { 12 int A[]={100,200,300,400,500}; 13 int B[]={10,20,30,40,50}; 14 int C[]; C=mystery(B); 17 if (C==A) { 18 System.out.println("same"); 19 } else { 20 System.out.println("different"); 21 } 22 } 23 } Answer different. == on references compares locations of what s being referenced, not the content of what s being referenced

26 1 public class Mystery08 { 2 public static final int SIZE=10; 3 public static void func(int A[], int B[], int x) { 4 for (int i=0; i<b.length; i++) { 5 B[i]=A[i]+B[i]+x; 6 } 7 A=B; 8 } 9 public static void main(string args[]) { 10 int []A = new int[size]; 11 int []B = new int[size]; for (int i=0; i<a.length; i++) { 14 A[i]=i; 15 B[i]=i*10; 16 } 17 func(a, B, 7); 18 System.out.println(A[1]); 19 } 20 }

27 1 public class Mystery08 { 2 public static final int SIZE=10; 3 public static void func(int A[], int B[], int x) { 4 for (int i=0; i<b.length; i++) { 5 B[i]=A[i]+B[i]+x; 6 } 7 A=B; 8 } 9 public static void main(string args[]) { 10 int []A = new int[size]; 11 int []B = new int[size]; for (int i=0; i<a.length; i++) { 14 A[i]=i; 15 B[i]=i*10; 16 } 17 func(a, B, 7); 18 System.out.println(A[1]); 19 } 20 } Answer

28 Write the few lines of code that prints all of the integers from 500 to 5000 that are evenly divisible by 7 using a for loop, while loop, and do-while loop.

29 Write the few lines of code that prints all of the integers from 500 to 5000 that are evenly divisible by 7 using a for loop, while loop, and do-while loop. for (int i=500; i<=5000; i++) { if (i%7==0) System.out.println(i); } int i=500; while (i<=5000) { if (i%7==0) System.out.println(i); i++; } int i=500; do { if (i%7==0) System.out.println(i); i++; } while (i<=5000);

30 Write the single line of code which declares a two-dimensional array of double with NCOL columns and NROW rows.

31 Write the single line of code which declares a two-dimensional array of double with NCOL columns and NROW rows. Answer double A[][]=new double[ncol][nrow]; or double [][]A=new double[ncol][nrow];

32 Write a method which is passed an array of int[ ] A and an int t (for threshold). The method returns the number of odd items in A which are greater than or equal to t. Write a method which is passed a two dimensional array of int A[][], and an int t. The method returns the index of the row in A which contains the greatest number of odd numbers greater than or equal to t. The method returns -1 if no row has any odd numbers greater than t. You may use your answer to part a in your answer to this part.