Characters and Strings

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Characters and Strings

• Chapter 7
• Dr. James Jiang

Characters and Strings
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String class

• Defined in java.lang.String
• String aGreeting new String(Hello)
• OR
• String aGreeting Hello

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Comparing Strings

• String variable name is a reference to a location
  in memory
• String aGreeting Hello
• aGreeting Bonjour

aGreeting holds an address that points to
Hello aGreeting holds a new address that points
to Bonjour
The garbage collector will discard Hello
Strings and other objects that cant be changed
are known as immutable
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The equals() method

• Evaluates the contents of two String objects to
  see if they are the same
• Method returns boolean true if equivalent

if(aName.equals(anotherName))
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The equalsIgnoreCase() method

• Evaluates the contents of two String objects to
  see if they are the same
• Ignores the case of the letters

aName DEBBIE anotherName
Debbie if(aName.equalsIgnoreCase(anotherName))
Returns true
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The compareTo() method

• Returns 0 if strings are equal
• negative ? calling less than argument
• positive I? calling greater than argument
• Example aName Roger
• aName.compareTo(Robert) ? 5
• For alphabetical order
• if(aWord.compareTo(anotherWord)
• aWord hamster anotherWord iguana

Returns true
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Other String Methods

• toUpperCase()
• aWord something
• aWord aWord.toUpperCase()
• toLowerCase()
• indexOf()
• String myName Stacy
• myName.indexOf(a) myName.indexOf(q)
• charAt()
• myName.charAt(0)

Results?
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Other String Methods

• endsWith()
• myName.startsWith(Sta) returns True
• replace()

String yourName Annette String goofyName
yourName.replace(n, X)
AXXette
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toString() Method

• Converts primitive type to a String
• How do we know that toString() is an overloaded
  method?

int someInt 4 theString Integer.toString(some
Int)
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subString() Method

• subString(start position, end position)

String dayOfWeek Monday, Tuesday,
Wednesday, Thursday, Friday String
sentence int x for(x 0 x x) sentence The abbreviation for
dayOfWeekx is dayOfWeekx.substring(0,3
) System.out.println(sentence)
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Converting Strings to Integers

• To convert a String to an integer, use the
  Integer class
• parseInt() is a method of the Integer class
• anInt Integer.parseInt(649)

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Converting Strings to Doubles

• To convert a String to a double, use the Double
  class
• double dvalue Double.parseDouble(147.82)
• valueOf()and doubleValue() are methods of the
  Double class
• String stringValue new String(147.82)
• Double tempValue Double.valueOf(stringValue)
• double doubleValue tempvalue.doubleValue()

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Example of Input

• import java.swing.x
• public class NumIn
• public static void main(String args)
• String inputString
• int inputNumber
• inputString JOptionPane.showInputDialo
  g(null, Enter the number)
• inputNumber Integer.parseInt(inputStri
  ng)
• if (inputNumber 100)
• JOptionPane.showMessageDialog(null,
  A surchage will apply)
• System.exit(0)