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Chapter 21 Collections 1205 58 // compare array contents 59 public void printEquality() 60 { 61 boolean b = Arrays.equals( intValues, intValuesCopy ); 62 63 System.out.println( “intValues ” + ( b ? “==” : “!=” ) 64 + ” intValuesCopy” ); 65 66 b = Arrays.equals( intValues, filledInt ); 67 68 System.out.println( “intValues ” + ( b ? “==” : “!=” ) 69 + ” filledInt” ); 70 } 71 72 // execute application 73 public static void main( String args[] ) 74 { 75 UsingArrays usingArrays = new UsingArrays(); 76 77 usingArrays.printArrays(); 78 usingArrays.printEquality(); 79 80 int location = usingArrays.searchForInt( 5 ); 81 System.out.println( ( location >= 0 ? 82 “Found 5 at element ” + location : “5 not found” ) + 83 ” in intValues” ); 84 85 location = usingArrays.searchForInt( 8763 ); 86 System.out.println( ( location >= 0 ? 87 “Found 8763 at element ” + location : 88 “8763 not found” ) + ” in intValues” ); 89 } 90 91 } // end class UsingArrays doubleValues: 0.2 3.4 7.9 8.4 9.3 intValues: 1 2 3 4 5 6 filledInt: 7 7 7 7 7 7 7 7 7 7 intValuesCopy: 1 2 3 4 5 6 intValues == intValuesCopy intValues != filledInt Found 5 at element 4 in intValues 8763 not found in intValues Fig. 21.1Using methods of class Arrays(part 3 of 3). Fig. 21.1 Line 18 calls Arrays static method fill to populate all 10 elements of array filledInt with 7s. Overloaded versions of fill allow the programmer to populate a specific range of elements with the same value. Line 20 sorts the elements of array doubleValues. Overloaded versions of sort allow the programmer to sort a specific range of elements. Arrays static method sortorders the array s elements in ascending order by default. We discuss how to sort in descending order later in the chapter. Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/12/01
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1204 Collections Chapter 21 6 7 public class UsingArrays { 8 private int intValues[] = { 1, 2, 3, 4, 5, 6 }; 9 private double doubleValues[] = { 8.4, 9.3, 0.2, 7.9, 3.4 }; 10 private int filledInt[], intValuesCopy[]; 11 12 // initialize arrays 13 public UsingArrays() 14 { 15 filledInt = new int[ 10 ]; 16 intValuesCopy = new int[ intValues.length ]; 17 18 Arrays.fill( filledInt, 7 ); // fill with 7s 19 20 Arrays.sort( doubleValues ); // sort doubleValues 21 22 System.arraycopy( intValues, 0, intValuesCopy, 23 0, intValues.length ); 24 } 25 26 // output values in each array 27 public void printArrays() 28 { 29 System.out.print( “doubleValues: ” ); 30 31 for ( int count = 0; count < doubleValues.length; count++ ) 32 System.out.print( doubleValues[ count ] + " " ); 33 34 System.out.print( "nintValues: " ); 35 36 for ( int count = 0; count < intValues.length; count++ ) 37 System.out.print( intValues[ count ] + " " ); 38 39 System.out.print( "nfilledInt: " ); 40 41 for ( int count = 0; count < filledInt.length; count++ ) 42 System.out.print( filledInt[ count ] + " " ); 43 44 System.out.print( "nintValuesCopy: " ); 45 46 for ( int count = 0; count < intValuesCopy.length; count++ ) 47 System.out.print( intValuesCopy[ count ] + " " ); 48 49 System.out.println(); 50 } 51 52 // find value in array intValues 53 public int searchForInt( int value ) 54 { 55 return Arrays.binarySearch( intValues, value ); 56 } 57 Fig. 21.1Using methods of class Arrays(part 2 of 3). Fig. 21.1 Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/12/01
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Chapter 21 Collections 1203 which is called the Standard Template Library (STL). (See Chapter 20 of C++ How to Program, Third Edition, by H. M. Deitel and P. J. Deitel, 2001, Prentice Hall). The Java collections framework provides ready-to-go, reusable componentry; you do not need to write your own collection classes. The collections are standardized so applications can share them easily, without having to be concerned with the details of their implementation. These collections are written for broad reuse. They are tuned for rapid execution as well as efficient use of memory. The collections framework encourages further reusability. As new data structures and algorithms are developed that fit this framework, a large base of programmers already will be familiar with the interfaces and algorithms implemented by those data structures. 21.2 Collections Overview A collection is a data structure actually, an object that can hold other objects. The collection interfaces define the operations that a program can perform on each type of collection. The collection implementations execute the operations in particular ways, some more appropriate than others for specific kinds of applications. Thecollection implementations are carefully constructed for rapid execution and efficient use of memory. Collections encourage software reuse by providing convenient functionality. The collections framework provides interfaces that define the operations to be performed generically on various types of collections. Some of the interfaces are Collection, Set, List and Map. Several implementations of these interfaces are provided within the framework. Programmers may also provide implementations specific to their own requirements. The collections framework includes a number of other features that minimize the amount of coding programmers need to do to create and manipulate collections. The classes and interfaces that comprise the collections framework are members of package java.util. In the next section, we begin our discussion by examining the capabilities that have been added for array manipulation. 21.3 Class Arrays We begin our discussion of the collections framework by looking at class Arrays, which provides static methods for manipulating arrays. In Chapter 7, our discussion of array manipulation was low level, in the sense that we wrote the actual code to sort and search arrays. Class Arrays provides high-level methods, such as binarySearch for searching a sorted array, equals for comparing arrays, fill for placing values into an array and sort for sorting an array. These methods are overloaded for primitive-type arrays and Objectarrays. Figure 21.1 demonstrates the use of these methods. 1 // Fig. 21.1: UsingArrays.java 2 // Using Java arrays. 4 // Java core packages 5 import java.util.*; Fig. 21.1Using methods of class Arrays(part 1 of 3). Fig. 21.1 Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/12/01
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1202 Collections Chapter 21 Outline 21.1 Introduction 21.2 Collections Overview 21.3 Class Arrays 21.4 Interface Collection and Class Collections 21.5 Lists 21.6 Algorithms 21.6.1 Algorithm sort 21.6.2 Algorithm shuffle 21.6.3 Algorithms reverse, fill, copy, max and min 21.6.4 Algorithm binarySearch 21.7 Sets 21.8 Maps 21.9 Synchronization Wrappers 21.10 Unmodifiable Wrappers 21.11 Abstract Implementations 21.12 (Optional) Discovering Design Patterns: Design Patterns Used in Package java.util Summary Terminology Self-Review Exercises Answers to Self-Review Exercises Exercises 21.1 Introduction In Chapter 19, we discussed how to create and manipulate data structures. The discussion was low level, in the sense that we painstakingly created each element of each data structure dynamically with new and modified the data structures by directly manipulating their elements and references to their elements. In this chapter, we consider the Java collections framework, which gives the programmer access to prepackaged data structures, as well as algorithms for manipulating those data structures. With collections, instead of creating data structures, the programmer simply uses existing data structures, without concern for how the data structures are implemented. This methodology is a marvelous example of code reuse. Programmers can code faster and can expect excellent performance, maximizing execution speed and minimizing memory consumption. We will discuss the interfaces of the collections framework, the implementation classes, the algorithms that process them and the iterators that walk through them. Some examples of collections are the cards you hold in a card game, your favorite songs stored in your computer and the real-estate records in your local registry of deeds (which map book numbers and page numbers to property owners). Java 2 provides an entire collections framework, whereas earlier versions of Java provided just a few collection classes, such as Hashtable, Stack and Vector (see Chapter 20), as well as built-in array capabilities. If you know C++, you will be familiar with its collections framework, Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/12/01
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21 Collections Objectives To understand what collections are. To understand Java 2 s new array capabilities. To use the collections framework implementations. To be able to use collections framework algorithms to manipulate various collections. To be able to use the collections framework interfaces to program polymorphically. To be able to use iterators to walk through the elements of a collection. To understand synchronization wrappers and modifiability wrappers. I think this is the most extraordinary collection of talent, of human knowledge, that has ever been gathered together at the White House with the possible exception of when Thomas Jefferson dines alone. John F. Kennedy The shapes a bright container can contain! Theodore Roethke Journey over all the universe in a map. Miguel de Cervantes It is an immutable law in business that words are words, explanations are explanations, promises are promises but only performance is reality. Harold S. Green Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/12/01
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1200 Java Utilities Package and Bit Manipulation Chapter 20 bits before and after each shift operation. Run your program once with a positive integer and once with a negative integer. 20.18 Show how shifting an integer left by 1 can be used to simulate multiplication by 2 and how shifting an integer right by 2 can be used to simulate division by 2. Be careful to consider issues related to the sign of an integer. 20.19 Write a program that reverses the order of the bits in an integer value. The program should input the value from the user and call method reverseBits to print the bits in reverse order. Print the value in bits both before and after the bits are reversed to confirm that the bits are reversed properly. You might want to implement both a recursive and an iterative solution. 20.20 Modify your solution to Exercise 19.10 to use class Stack. 20.21 Modify your solution to Exercise 19.12 to use class Stack. 20.22 Modify your solution to Exercise 19.13 to use class Stack.
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Chapter 20 Java Utilities Package and Bit Manipulation 1199 e) containsKey f) contains g) clear h) elements i) keys 20.12 Explain how to use the Random class to create pseudorandom numbers with the repeatability required for debugging purposes. 20.13 Use a Hashtable to create a reusable class for choosing one of the 13 predefined colors in class Color. The name of the color should be used as keys and the predefined Color objects should be used as values. Place this class in a package that can be imported into any Java program. Use your new class in an application that allows the user to select a color and draw a shape in that color. 20.14 Modify your solution to Exercise 13.18 the polymorphic painting program to store every shape the user draws in a Vectorof MyShapeobjects. For the purpose of this exercise, create your own Vector subclass called ShapeVector that manipulates only MyShape objects. Provide the following capabilities in your program: a) Allow the user of the program to remove any number of shapes from the Vector by clicking an Undo button. b) Allow the user to select any shape on the screen and move it to a new location. This requires the addition of a new method to the MyShape hierarchy. The method s first line should be public boolean isInside() This method should be overridden for each subclass of MyShape to determine whether the coordinates where the user pressed the mouse button are inside the shape. c) Allow the user to select any shape on the screen and change its color. d) Allow the user to select any shape on the screen that can be filled or unfilled and change its fill state. 20.15 What does it mean when we state that a Propertiesobject is a persistent Hashtable object? Explain the operation of each of the following methods of the Properties class: a) load b) store c) getProperty d) propertyNames e) list 20.16 Why might you want to use objects of class BitSet? Explain the operation of each of the following methods of class BitSet: a) set b) clear c) get d) and e) or f) xor g) size h) equals i) clone j) toString k) hashCode 20.17 Write a program that right shifts an integer variable 4 bits with sign extension and then right shifts the same integer variable 4 bits with zero extension. The program should print the integer in
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1198 Java Utilities Package and Bit Manipulation Chapter 20 tor increases, there are fewer available slots relative to the total number of slots, so the chance of selecting an occupied slot (a collision) with a hashing operation increases. 20.3 When a program calls popor peekon an empty Stack object, an EmptyStackException occurs. 20.4 a) bitwise AND (&). b) bitwise inclusive OR (|). c) bitwise exclusive OR (^). d) mask. e) left shift operator (<<). f) right shift operator with sign extension (>>), right shift operator with zero extension (>>>). EXERCISES 20.5 Define each of the following terms in the context of hashing: a) key b) collision c) hashing transformation d) load factor e) space time trade-off f) Hashtable class g) capacity of a Hashtable 20.6 Explain briefly the operation of each of the following methods of class Vector: a) addElement b) insertElementAt c) setElementAt d) removeElement e) removeAllElements f) removeElementAt g) firstElement h) lastElement i) isEmpty j) contains k) indexOf l) trimToSize m) size n) capacity 20.7 Explain why inserting additional elements into a Vector object whose current size is less than its capacity is a relatively fast operation and why inserting additional elements into a Vector object whose current size is at capacity is a relatively slow operation. 20.8 In the text, we state that the default capacity increment of doubling the size of a Vector might seem wasteful of storage, but it is actually an efficient way for Vectors to grow quickly to be about the right size. Explain this statement. Explain the pros and cons of this doubling algorithm. What can a program do when it determines that the doubling is wasting space? 20.9 Explain the use of the Enumeration interface with objects of class Vector. 20.10 By extending class Vector, Java s designers were able to create class Stack quickly. What are the negative aspects of this use of inheritance, particularly for class Stack? 20.11 Explain briefly the operation of each of the following methods of class Hashtable: a) put b) get c) remove d) isEmpty
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Chapter 20 Java Utilities Package and Bit Manipulation 1197 nextLong method of class Random removeElementAt method of class Vector NoSuchElementException class search method of class Stack NullPointerException seed of a random-number generator or method of class BitSet set method of class BitSet peek method of class Stack setElementAt method of class Vector persistent hash table setSeed method of class Random pop method of class Stack setSize method of class Vector Properties class size method of class Dictionary propertyNamesmethod of Properties size method of class Vector pseudorandom numbers Stack class push method of class Stack store method of class Properties put method of class Dictionary trimToSize method of class Vector Random class Vector class remove method of class Dictionary white-space characters removeAllElementsmethod of Vector xor method of class BitSet removeElement method of class Vector SELF-REVIEW EXERCISES 20.1 Fill in the blanks in each of the following statements: a) Java class provides the capabilities of array-like data structures that can re- size themselves dynamically. b) If you do not specify a capacity increment, the system will the size of the Vector each time additional capacity is needed. c) If storage is at a premium, use the method of the Vector class to trim a Vector to its exact size. 20.2 State whether each of the following is true or false. If false, explain why. a) Values of primitive data types may be stored directly in a Vector. b) With hashing, as the load factor increases, the chance of collisions decreases. 20.3 Under what circumstances is an EmptyStackExceptionthrown? 20.4 Fill in the blanks in each of the following statements: a) Bits in the result of an expression using operator are set to 1 if the corresponding bits in each operand are set to 1. Otherwise, the bits are set to zero. b) Bits in the result of an expression using operator are set to 1 if at least one of the corresponding bits in either operand is set to 1. Otherwise, the bits are set to zero. c) Bits in the result of an expression using operator are set to 1 if exactly one of the corresponding bits in either operand is set to 1. Otherwise, the bits are set to zero. d) The bitwise AND operator (&) is often used to bits, that is, to select certain bits from a bit string while zeroing others. e) The operator is used to shift the bits of a value to the left. f) The operator shifts the bits of a value to the right with sign extension, and the operator shifts the bits of a value to the right with zero extension. ANSWERS TO SELF-REVIEW EXERCISES 20.1 a) Vector. b) double. c) trimToSize. 20.2 a) False; a Vector stores only Objects. A program must use the type-wrapper classes (Byte, Short, Integer, Long, Float, Double, Boolean and Character) from package java.lang to create Objects containing the primitive data type values. b) False; as the load fac
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1196 Java Utilities Package and Bit Manipulation Chapter 20 The right shift operator with zero extension (>>>) shifts the bits in its left operand to the right by the number of bits specified in its right operand 0s are shifted in from the left. The bitwise complement (~) operator sets all 0 bits in its operand to 1 in the result and sets all 1 bits to 0in the result. Each bitwise operator (except complement) has a corresponding assignment operator. The no-argument BitSet constructor creates an empty BitSet. The one-argument BitSet constructor creates a BitSet with the number of bits specified by its argument. BitSet method set sets the specified bit on. Method clear sets the specified bit off. Method get returns true if the bit is on, false if the bit is off. BitSet method and performs a bit-by-bit logical AND between BitSets. The result is stored in the BitSet that invoked the method. Similarly, bitwise logical OR and bitwise logical XOR are performed by methods or and xor. BitSet method size returns the size of a BitSet. Method toString converts a BitSetto a String. TERMINOLOGY addElement method of class Vector elements method of class Dictionary and method of class BitSet elements method of class Vector bit set EmptyStackException class BitSet class enumerate successive elements bitwise assignment operatorsEnumeration interface &= (bitwise AND)equals method of class Object ^= (bitwise exclusive OR)firstElement method of class Vector |= (bitwise inclusive OR) get method of class BitSet <<= (left shift) get method of class Dictionary >>= (right shift) getProperty method of class Properties >>>= (right shift with zero extension) hashCode method of class Object bitwise manipulation operatorshashing & bitwise ANDHashtable class ^ bitwise exclusive ORhasMoreElements method (Enumeration) | bitwise inclusive ORindexOf method of class Vector ~ one s complementinitial capacity of a Vector << left shiftinsertElementAt method of class Vector >> right shiftisEmpty method of class Dictionary >>> right shift with zero extension isEmpty method of class Vector capacity increment of a Vector iterate through container elements capacity method of class Vector java.util package capacity of a Vector key in a Dictionary clear method of class BitSet key/value pair clear method of class Hashtable keys method of class Dictionary clone method of class BitSet lastElement method of class Vector collision in hashing list method of class Properties contains method of class Vector load factor in hashing containsKey method of class Hashtable load method of class Properties defaults nextDouble method of class Random Dictionary class nextElement method of Enumeration dynamically resizable array nextFloat method of class Random elementAt method of class Vector nextInt method of class Random
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