java arrays …………. java arrays …………. * arrays are objects in java * arrays are...

Java Arrays ………….Java Arrays ………….

* arrays are * arrays are objectsobjects in Java in Java

* an array variable is a reference* an array variable is a reference

* an array must be instantiated * an array must be instantiated (created)(created)

An array can store primitive values………….

int[] myarr; // array reference

myarr = new int[5];

myarr

myarr[0] myarr[4]

int [] myarr = new int[5];

//initialize arrayString fiveletterword = JOptionPane.showInputDialog(“Enter 5 letter word”);for (int strpos=0; strpos < 5; strpos++) myarr[strpos] = fiveletterword.charAt(strpos); //what’s going on here

//print out the ASCII values in the arrayString temp = “”;for (int index=0; index < 5; index ++) temp = temp + “ “ + myarr[index]; System.out.println(temp); //what is printed, numbers or chars?

// using length field of an arrayfor (int index = 0; index < myarr.length; index ++) myarr[index] = 100;

Can also create an array object by providing initial values:

double[] values = { 5.5, 6.1, 0.0, 6.1, 4.3, 7.1};

values is an array of length 6, with legal indices 0 to 5

An array can be declared to store any type … class types too.

import java.io;public class demo{ public static void main (String [] xx) throws IOException {

String[] groceries = new String [100]; //each element of groceries is a reference to an object

FileReader instream = new FileReader(“list.txt”);BufferedReader in = new BufferedReader(instream);String item = in.readLine();int index = 0;

while (item != null) { groceries[index] = item; index++; item = in.readLine();}

bagelsbagelscoffeecoffee

FileReader instream = new FileReader(“list.txt”);BufferedReader in = new BufferedReader(instream);String item;int index = 0;

while ((item = in.readLine() )!= null) groceries[index++] = item; //alternative loop implementation

teatea

groceries

String objects……

Assuming the array groceries ..

What would the following print to the screen…….

for (int i= 0; i < groceries.length; i++) temp = temp + “ “ + groceries[i];

System.out.println(temp);

for (int i= 0; i < numItems; i++) temp = temp + “ “ + groceries[i];

System.out.println(temp);

coffee tea bagels null null null null null null null (90 more times)

String item = in.readLine(); //code which stored values in arrayint index = 0;int numItems = 0;

while (item != null) { groceries[index] = item; index++; item = in.readLine();}int numItems = index;

Each item of the array groceries is a String object, and can be usedto call String methods……

for (i=0; i < numItems; i++) groceries[i] = groceries[i].toUpperCase();

What would happen if I replaced numItems with groceries.length ??

The java.util package provides a class named Arrays. This class is full of STATIC METHODS which work with array parameters…………

http://java.sun.com/j2se/1.4.2/docs/api/index.html

Code which stores, sorts and then searches thru data is easy…….for (index = 0; index < numItems; index++) temp = temp + " " + groceries[index]; System.out.println("groceries are" + temp); String [] groceries2 = new String[numItems]; System.arraycopy(groceries,0, groceries2, 0, numItems); Arrays.sort(groceries2); //must sort and search full arraywhile ((item=JOptionPane.showInputDialog("Enter item to look for ")) != null){ index = Arrays.binarySearch(groceries2,item); if (index >=0 ) JOptionPane.showMessageDialog(null, item + " is there"); else JOptionPane.showMessageDialog(null, item + " is not there"); }

If I had an array of Dog objects, would I be able to sortand search ????????????

need to know about interfaces………………..