Arrays Chapter 7

2 Declaring and Creating Arrays Recall that an array is a collection of elements all of the _____________ Array objects in Java must be created with the key word _______________ Syntax int c[] = new int [12]; Results: –12 integer locations are allocated –They are _____________________ (null for reference variables, false for boolean)

3 Using Arrays View example Figure 7.2Figure 7.2 Note –Declaration of the array –Allocation of memory with new –Initialization of array elements –Use of array attribute ( _______________ ) –Printing of array contents

4 The Array Initializer A comma separated list of expressions –The ______________ list –Enclosed in _________________ View the ExampleExample –Note again, how the array knows its own _______ for (int count = 0 ; count < array.length ; count++)...

5 Processing Elements of An Array Finding and using the arithmetic mean –__________________ the array, create –Read in values, ___________________ –Declare a summation variable, initialize –______________ the array, calculate average –_______________ the array –Print results, accessing the array See sample programsample program

6 Histogram Program Use the value in the array to –Print the value –Print a string of asterisks for __________________ of size of the value View Figure 7.6,Figure 7.6

7 Using Array Elements as Counters Recall program which tested random number generator (Figure 6.8)Figure 6.8 –Used 6 different variables –Used switch statement to increment –At the time we noted the ________________ Consider a new version of the program –Uses _______________ to total the number of rolls of each number 1 – 6 –No ___________ statement needed View Figure 7.7Figure 7.7

8 Enhanced for Statement Enhanced for statement –New feature of J2SE 5.0 –Allows iterates through elements of an array or a collection _______________________ –Syntax for ( parameter : arrayName ) statement –View example, Figure 7.12Figure 7.12

9 References and Reference Parameters In Java, primitive-type variables are always passed by _________ –Incoming data only Objects are not passed to methods –__________ to objects are passed –The reference is passed by value With a reference to the object the method can _____________ the object directly

10 References and Reference Parameters Passing arrays by reference –Improves _______________ –Saves time ________________ of large array not required –Saves _______________ Use memory already occupied by array No new memory allocation required –View example program, Figure 7.13Figure 7.13

11 Using Arrays Sorting Arrays –Recall previous exampleprevious example Searching Arrays –________________ search (see example)example Step through array until desired value located –Binary search Array must be _________________ Look in middle, then above or below –Look in middle of sub-section then above or below –Etc.

12 Multidimensional Arrays Java does not support ________________ arrays directly Does allow declaration of arrays whose elements are ______________! int b[][]; b = new int[ 2 ][ ]; // allocate rows b[ 0 ] = new int[ 5 ]; // allocate columns for row 0 b[ 1 ] = new int[ 3 ]; // allocate columns for row 1

13 Fig | Two-dimensional array with three rows and four columns. Multidimensional Arrays

14 Creating Two-dimensional Arrays –Can be created dynamically –3 -by- 4 array int b[][]; b = new int[ 3 ][ 4 ]; –Rows can have different number of ____________ int b[][]; b = new int[ 2 ][ ]; // create 2 rows b[ 0 ] = new int[ 5 ]; // create 5 columns for row 0 b[ 1 ] = new int[ 3 ]; // create 3 columns for row

15 Variable-Length Argument Lists New feature in J2SE 5.0 ___________________ number of arguments Use ellipsis ( … ) in method’s parameter list –Can occur _______________ in parameter list –Must be placed at the __________ of parameter list Array whose elements are all of the same type View example, Fig. 7.20Fig. 7.20

16 Using Command-Line Arguments Pass arguments from the command line –String args[] Appear after the _____________ in the java command –java MyClass a b _________________ of arguments passed in from command line –args.length First command-line argument –args[ 0 ]