Lecture 11. Lecture

Transcription

1 Sor,ng Calcula,onApplet Java Examples Mergesort D0010E!! The GUI Containment Hierarchy! Arrays! Lecture 8 - Håkan Jonsson 2 Lecture 8 - Håkan Jonsson 3 1

2 1. Mul,dimensional arraya So far, we have seen declara,ons of array variables looking like <Type> [] <variable>; Example: Room[] rooms; We could then create an array and have the variable refer to it by wri,ng <variable> = new <Type> [ <size> ] Example: rooms = new Room[10]; And then we could start using the array: <variable> (rooms) <variable> [ <index> ] (rooms[3]) <variable>. length (rooms.length) - Håkan Jonsson 4 Mul,dimensional arrays In fact, we can have "arrays of arrays". <Type> [] [] [] <variable>; The number of pairs of brackets is the dimension. Example: ChessPiece[][][] chessboard3d;! A d- dimensional array = a 1- dimensional containing (d- 1)- dimensional arrays. - Håkan Jonsson 5 Mul,dimensional arrays Mul,dimensional arrays can be ragged. All arrays in some dimension need not be of equal length. It is possible to create a mul,- dimensional array in steps. - Håkan Jonsson 6 2

3 Ragged and nonragged Nonragged Ragged 1D 2D 2D 3D 2D Lecture 8 - Håkan Jonsson 7 Handling mul,dimensional arrays Ragged or not, subarrays can be referenced and assigned as long as their dimension fits the context. int[][] a = { {1, 2, 3}, {4, 5} }; A 2D array int[][] b = { {6, 7}, {8, 9, 0} }; A 2D array int[] c = {10, 11, 12, 13}; A 1D array int d = 14; A 0D array Assignment Dimensions a[1] = b[0]; A 1D array is assigned a 1D array b[1][2] = a[0][2]; A 0D array is assigned a 0D array c = a[0]; A 1D array is assigned a 1D array b[0] = c; A 1D array is assigned a 1D array a[1][1] = c[3]; A 0D array is assigned a 0D array b = a; A 2D array is assigned a 2D array d = c[2]; A 0D array is assigned a 0D array Lecture 8 - Håkan Jonsson 8 Lecture 8 - Håkan Jonsson 9 3

4 2. The GUI containment hierarchy Java s library contains classes with ready- made, commonly used graphical components like JPanel, JBu?on, JTextField, JLabel, etc Standard prac,ce is to extended (specialize via inheritance) these. JPanel is a both a container and a component. The various containers and their contents define a containment hierarchy. - Håkan Jonsson 10 Layouts The rela,ve sizes and posi,ons of GUI components and containers with respect to each other is governed by Layout managers. BorderLayout, GridLayout, GridBagLayout, SpringLayout etc. Each layout- manager posi,ons and re- sizes components according to a strategy of its own. Each container is assigned a default layout- manager when created. setlayout( ) can be used to change the layout- manager of a container. Every container in the containment hierarchy has a layout- manager of its own working within the premises of its parent layout- manager. - Håkan Jonsson 11 Containment Hierarchy 2 containers 4 components A layout- manager per container - Håkan Jonsson 12 4

5 Lecture 8 - Håkan Jonsson Hierarchical layouts A 5- part layout and design example using JApplet as top- container. The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. - Håkan Jonsson 14 Layout in CalculatorApplet ypanel xpanel xinput xinput yinput yinput plus minus,mes divides plus minus,mes divides answer answer content bumonpanel Lecture 8 - Håkan Jonsson 15 5

6 Layout managers Lecture 8 - Håkan Jonsson 16 Lecture 8 - Håkan Jonsson Increasing locality Weakness: The if statements in the acfonperformed method. Whenever a new bumon is added in init, we must remember to (also) add another if statement. The bumons are rather unac,ve. Solu,on: Tailor- make the bumons and have them govern what happens/is displayed when they are pressed through a common behavior. We achieve this by introducing an abstract super class BinaryOperatorBu?on that concrete bumon classes then extend. - Håkan Jonsson 18 6

7 UML for BinaryOperatorBu?on l11.calc.buttons! Here, the Template Design Pa?ern is used to create (concrete) alternafve bu?on classes based on another (abstract) bu?on class. The abstract method result is used in tostring and supposed to be implemented by the bu?on classes. - Håkan Jonsson 19 Example: MyCalculatorApplet1 Lecture 8 - Håkan Jonsson 20 Lecture 8 - Håkan Jonsson 21 7

8 5. Adding new bumons Let's add a bumon to compute x y. This is done in MyCalculatorApplet2. package l11.calc.buttons;!! public class Power extends BinaryOperatorButton {!! public Power(String s) {! super(s);! }!! protected String result(double x, double y) {! return "" + (java.lang.math.pow(x, y));! }! }! - Håkan Jonsson 22 Example: MyCalculatorApplet2 - Håkan Jonsson 23 Lecture 8 - Håkan Jonsson 24 8

9 6. Design by delega,on (Note that although they can not be used directly, abstract classes can contain concrete constructors.) Lecture 8 - Håkan Jonsson 25 Example: MyCalculatorApplet3 New bumon classes. Same names though, but a different package (calc2). (Slightly) new way to create bumons. Two more arguments. Less code to repeat. - Håkan Jonsson 26 Lecture 8 - Håkan Jonsson 27 9

10 7. Immediately adding bumons We only create one (1) bumon of each class. We could use anonymous classes. In fact, none of the subclasses Plus, Minus, Times, etc are needed, only BinaryOperatorBu?on.) This is how we could add a bumon to compute the length of the (math) vector from origo to (x,y): The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Lecture 8 - Håkan Jonsson 28 Example: MyCalculatorApplet4 Lecture 8 - Håkan Jonsson 29 Lecture 8 - Håkan Jonsson 30 10

11 8. Sor,ng The problem of sor,ng is fundamental in compu,ng as (very) large parts of what computers do today is to "sort". By sorfng is meant the re- arrangement of the elements in a sequence so they occur in order. Sor,ng 3,5,1,2,4 results in 1,2,3,4,5. All sequences containing comparable elements can be sorted. In Java, a sequence can be an array or vector, for example. - Håkan Jonsson 31 Comparable - Håkan Jonsson 32 - Håkan Jonsson 33 11

12 Lecture 8 - Håkan Jonsson Mergesort Mergesort is a algorithm to sort based on divide and conquer. Used (most likely also invented) by John von Neumann to program ENIAC in Informally, Mergesort works as follows: 1. Divide the unsorted set into two halves. 2. Sort each half. Use Mergesort twice here (recursively). 3. Merge the two results into sorted order Håkan Jonsson More about Mergesort Source: Wikipedia Lecture 8 - Håkan Jonsson 36 12

13 Example: mergesort 1) Wri,ng... <T extends Comparable<T>>... means T is a class that implements Comparable<T>. In prac,ce, the class contains a method compareto the method compares dynamic objects of the type defined by the class. Example: public stafc <T extends Comparable<T>> void mergesort(t[] a) 2) This is not possible in Java: T[] t = new T[10]; 3) To make a copy of a generic array, there is the method public stafc <T> T[] copyof(t[] original, int newlength) in the class java.ufl.arrays. - Håkan Jonsson 37 Lecture 8 - Håkan Jonsson 38 13