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Arrays

Arrays. Background. Programmer often need the ability to represent a group of values as a list List may be one-dimensional or multidimensional Java provides arrays and the collection classes The Vector class is an example of a collection class Consider arrays first. Basic terminology.

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Arrays

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  1. Arrays

  2. Background • Programmer often need the ability to represent a group of values as a list • List may be one-dimensional or multidimensional • Java provides arrays and the collection classes • The Vector class is an example of a collection class • Consider arrays first

  3. Basic terminology • List is composed of elements • Elements in a list have a common name • The list as a whole is referenced through the common name • List elements are of the same type — the base type • Elements of a list are referenced by subscripting (indexing) the common name

  4. Java array features • Subscripts are denoted as expressions within brackets: [ ] • Base (element) type can be any type • Size of array can be specified at run time • This is different that pure C! (for the most part, at least) • Index type is integer and the index range must be 0 ... n-1 • Where n is the number of elements • Automatic bounds checking • Ensures any reference to an array element is valid • Data field length specifies the number of elements in the list • Array is an object • Has features common to all other objects

  5. ElementType [ ] id; Brackets Name of Type of indicate array list values in variable being list defined Array variable definition styles • Without initialization int [] a; int a[];

  6. Nonnegative integer expression specifying the number of elements in the array ElementType id ElementType [n]; = new [ ] Reference to a new array of n elements Array variable definition styles • With initialization

  7. c - … value 0 0 0 0 0 Example • Definitions char[] c; int[] value = new int[10]; • Causes • Array object variable c is un-initialized • Array object variable v references a new ten element list of integers • Each of the integers is default initialized to 0

  8. 2004 IOCCC winners • 2004 winners: • 2004 anonymous Rendering of a stroked font • 2004 arachnid Curses maze displayer/navigator with only line-of-sight visibility • 2004 burley A Poker game • 2004 gavare A ray tracer • 2004 gavin Mini-OS • 2004 hibachi A CGI capable HTTP server • 2004 hoyle Curses based polynomial graphing with auto-scale • 2004 jdalbec Conway's look'n'say sequence split into elements • 2004 kopczynski OCR of 8, 9, 10 and 11 • 2004 newbern Renders arbitary bitmapped fonts • 2004 omoikane A CRC inserter • 2004 schnitzi Editor animation • 2004 sds Space/tab/linefeed steganography • 2004 vik1 X Windows car racing game • 2004 vik2 Calculates prime numbers using only CPP • At http://www1.us.ioccc.org/years.html#2004

  9. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  10. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  11. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  12. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  13. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  14. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  15. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt();

  16. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt(); 8 is displayed

  17. Consider int[] v = new int[10]; int i = 7; int j = 2; int k = 4; v[0] = 1; v[i] = 5; v[j] = v[i] + 3; v[j+1] = v[i] + v[0]; v[v[j]] = 12; System.out.println(v[2]); v[k] = stdin.nextInt(); Suppose 3 is extracted

  18. Consider • Segment int[] b = new int[100]; b[-1] = 0; b[100] = 0; • Causes • Array variable to reference a new list of 100 integers • Each element is initialized to 0 • Two exceptions to be thrown • -1 is not a valid index – too small • 100 is not a valid index – too large • IndexOutOfBoundsException

  19. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  20. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  21. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  22. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  23. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  24. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  25. Consider Point[] p = new Point[3]; p[0] = new Point(0, 0); p[1] = new Point(1, 1); p[2] = new Point(2, 2); p[0].setX(1); p[1].setY(p[2].getY()); Point vertex = new Point(4,4); p[1] = p[0]; p[2] = vertex;

  26. id references an array of n elements. id[0] has value exp0, id[1] has value exp1, and so on. Each expiis an expression that evaluates to type ElementType Explicit initialization • Syntax ElementType id exp , exp , ... exp [] = { } ; 0 1 -1 n

  27. Explicit initialization • Example String[] puppy = { “pika“, “arlo“, “shadow", “lucia" }; int[] unit = { 1 }; • Equivalent to String[] puppy = new String[4]; puppy[0] = “pika"; puppy[1] = “arlo"; puppy[2] = “shadow"; puppy[4] = “lucia"; int[] unit = new int[1]; unit[0] = 1;

  28. Empty set: an example

  29. Array members • Member length • Size of the array for (int i = 0; i < puppy.length; ++i) { System.out.println(puppy[i]); }

  30. Array members • Member clone() • Produces a shallow copy Point[] u = { new Point(0, 0), new Point(1, 1)}; Point[] v = u.clone(); v[1] = new Point(4, 30);

  31. Array members • Member clone() • Produces a shallow copy Point[] u = { new Point(0, 0), new Point(1, 1)}; Point[] v = u.clone(); v[1] = new Point(4, 30);

  32. Array members • Member clone() • Produces a shallow copy Point[] u = { new Point(0, 0), new Point(1, 1)}; Point[] v = u.clone(); v[1] = new Point(4, 30);

  33. Array members • Member clone() • Produces a shallow copy Point[] u = { new Point(0, 0), new Point(1, 1)}; Point[] v = u.clone(); v[1] = new Point(4, 30);

  34. Making a deep copy • Example Point[] w = new Point[u.length]; for (int i = 0; i < u.length; ++i) { w[i] = (Point) u[i].clone(); }

  35. Making a deep copy

  36. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  37. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  38. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  39. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  40. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  41. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  42. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  43. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  44. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  45. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  46. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  47. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  48. Searching for a value System.out.println("Enter search value (number): "); int key = stdin.nextInt(); int i; for (i = 0; i < data.length; ++i) { if (key == data[i]) { break; } } if (i != data.length) { System.out.println(key + " is the " + I + "-th element"); } else { System.out.println(key + " is not in the list"); }

  49. Searching for the minimum value • Segment int minimumSoFar = sample[0]; for (int i = 1; i < sample.length; ++i) { if (sample[i] < minimumSoFar) { minimumSoFar = sample[i]; } }

  50. ArrayTools.java method sequentialSearch() publicstaticintsequentialSearch(int[]data,int key){ for (int i = 0; i < data.length; ++i) { if (data[i] == key) { return i; } } return -1; } • Consider int[] score = {6,9,82,11,29,85,11,28, 91}; int i1 = sequentialSearch(score,11); int i2 = sequentialSearch(score,30);

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