Objectives ► Become familiar with the class String ► ► Learn how to use input and output dialog boxes in a program ► ► Learn how to tokenize the input stream ► Explore how to format the output of decimal numbers with the class DecimalFormat

Object and Reference Variables ► Declare a reference variable of a class type ► Use the operator new to:  Allocate memory space for data  Instantiate an object of that class type ► Store the address of the object in a reference variable

The Operator new ► Statement: Integer num; num = new Integer(78); ► Result:

Garbage Collection ► Change value of num: num = new Integer(50); ► Old memory space reclaimed

Using Predefined Classes and Methods in a Program ► Many predefined packages, classes, methods in Java ► Library: Collection of packages ► Package: Contains several classes ► Class: Contains several methods ► Method: Set of instructions

Using Predefined Classes and Methods in a Program ► To use a method you must know:  Name of class containing method (Math)  Name of package containing class (java.lang)  Name of method (pow), its parameters (int a, int b), and the function or purpose of the method (a^b) int i=2 j=4, k; k= Math.pow( i, j ); The value of k will be 2^4=16

Using Predefined Classes and Methods in a Program ► Example method call: import java.io.*; //imports package OR import java.io.BufferReader: //imports class Math.pow(2,3); //calls power method in //class Math or package java.lang Package java.lang is automatically imported ► (Dot). Operator: used to access the method in the class

The class String ► String variables are reference variables ► Given String name;  Equivalent Statements: name = new String("Lisa Johnson"); name = “Lisa Johnson”;

Commonly Used String Methods ► String(String str) ► char charAt(int index) ► int indexOf(char ch) ► int indexOf(String str, int pos) ► int compareTo(String str)

Commonly Used String Methods ► String concat(String str) ► boolean equals(String str) ► int length() ► String replace(char ToBeReplaced, char ReplacedWith) ► String toLowerCase() ► String toUpperCase()

What is tokenizing ► Consider the following string  “This is a test of string tokenizing” ► A token is a substring of this string that is selected as follows:  A particular delimeter or separation character is chosen, in this case choose whitespace (blank or tab)  Starting at the beginning of the string characters are added to the substring until a delimeter is encountered  The token is the substring (the delimeter is not added to the substring)

What is tokenizing ► The next token is selected as follows:  The next character in the string that is not a delimeter is located. This character is the first character of the next token.  Starting at this character, additional characters are added to the substring until a delimeter is encountered  The token is the substring (the delimeter is not added to the substring) ► For this example the second token would be “is” ► The pattern continues until all characters in the string have been processed.

Tokenizing a String ► class StringTokenizer  Contained in package java.util  Tokens usually delimited by whitespace characters (space, tab, newline, etc)  Contains methods: ► public StringTokenizer(String str, String delimits) ► public int countTokens() ► public boolean hasMoreTokens() ► public String nextToken(String delimits)

StringTokenizer tokenizer; String inputLine; String name; String number; inputLine = “Judy 3250”; tokenizer = new StringTokenizer(inputLine); name = tokenizer.nextToken(); num = Integer.parseInt( tokenizer.nextToken() );

Using Dialog Boxes for Input/Output ► Use a graphical user interface (GUI) ► class JOptionPane  Contained in package javax.swing  Contains methods: showInputDialog and showMessageDialog ► Syntax: str = JOptionPane.showInputDialog(strExpression) ► Program must end with System.exit(0);

Parameters for the Method showMessageDialog

JOptionPane Options for the Parameter messageType

JOptionPane Example

Formatting the Output of Decimal Numbers ► Type float: defaults to 6 decimal places ► Type double: defaults to 15 decimal places

class Decimal Format ► Import package java.text ► Create DecimalFormat object and initialize ► Use method format ► Example: DecimalFormat twoDecimal = new DecimalFormat("0.00"); twoDecimal.format(56.379); ► Result: 56.38