Chapter 6

Section 6.1

• an array is a list of values, each stored at a specific numbered position in the array
• the numbered position is the array index or subscript
• indexes always begin at zero
• to access value in array, use array name followed by index in [ ]
• if it’s an array of integers, each value in it is just an integer, so can be used anywhere a normal integer is used
• array indexes are just integers too, so can use integer expressions to calculate them as well
• arrays are objects – to create an array the reference must be declared
• then array can be instantiated using new to allocate memory space
• ex. int[] height = new int[11];
• type is int[] – doesn’t include size
• once array is declared a certain size, size can’t be changed
• listing 6.1
• [] are an operator – have highest precedence of all operators
• performs automatic bounds checking – ensures index is in range of array size
• index must be >= 0 and < size of array – otherwise ArrayIndexOutOfBoundsException is thrown
• array size is held in constant called length – public constant that can be referenced
• listing 6.2, 6.3
• can declare arrays as int[] grade or int grade[] – book uses first for consistency
• initializer list lists initial values of array on declaration – used instead of new
• listing 6.4
• entire array can be passed as parameter – it is an object, so copy of reference to original array is passed
• so method can change element of array permanently, just not the reference itself
• can pass just an element of an array to a method, too

Section 6.2

• arrays can have references to objects as elements
• ex. String[] words = new String[25];
• this doesn’t create any String objects, just an array to hold 25 of them
• listing 6.5
• parameter to main is always an array of String objects
• main is invoked when application is submitted to an interpreter – String[] parameter args represents any command-line arguments that might be provided
• listing 6.6
• creation of array and creation of objects in array are very different
• listing 6.7, 6.8. 6.9

Section 6.3

• sorting is process of arranging a list into some order
• selection sort sorts by repeatedly putting a value in the list into its final sorted position – uses swapping
• listing 6.10, 6.11
• insertion sort sorts by repeatedly inserting a value into a subset of sorted values
• listing 6.12, 6.13
• compare sorting algorithms for efficiency – considered less efficient if it performs more compares
• both have an outer and inner loop , so perform n-squared comparisons for n values in the list (order n-squared)

Section 6.4

• two-dimensional arrays have values in two dimensions
• use two indexes, one for rows and one for columns
• declare as int[][] - an array of arrays
• can also initialize with initializer list
• listing 6.14, 6.15
• arrays can be multi-dimensional too

Section 6.5

• Vector class works like arrays and can store a list of values and reference them by an index
• it can dynamically grow and shrink
• isn’t declared to store a particular type – manages list of references to Objects
• listing 6.16
• indexes adjust accordingly when elements are inserted or deleted
• objects in a Vector object can be of different reference types
• implemented using arrays
• elements can be added without allocating more memory until it reaches capacity, then capacity is expanded

Section 6.6

• polygon is multisided shape – defined with a series of x,y points for endpoints of lines in polygon
• polygon is always closed
• polylines don’t have to be closed, so can’t be filled
• listing 6.17
• Polygon class
• to save the state of a drawing and not clear and redraw every repaint call, keep track of all necessary information in an array or vector
• listing 6.18