Transcript Class and Object

String class
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Construct a string
String str = new String(“welcome”);
Char[] charr = {‘G’, ‘o’, ‘o’, ‘d’};
String mes = new String(charr);
A full list of String class methods and
constructors P259 Chapter 7.2
Some String methods
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int length()
String subString( int beginindex)
String toLowerCase()
String concat( String )
char chatAt( ont index)
boolean equals( String anotherString)
continue
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String concatenation
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String s3 = s1.concat(s2);
S3 = s1 + s2;
S3 = message + “and “+ “HTML”;
Extracting substring
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String message = “Welcome to
Java”.subString(1,11) + “HTML”;
continued
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String comparisons
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If( string1 == string2)
Will check if string1 and string 2 refer to same
object
To find out whether two string objects have
same content, use equals()
If( string1.equals(string2))
S1.compareTo(s2) return 0 if s1 is equals to s2,
less than 0 if s1 is lexicographically less than s2,
and greater than 0 if s1 is lexicographically
greater than s2
Can be used in sorting algorithm
Finding a character in a string
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int indexOf( int ch)
“welcome to Java”.indexOf(‘w’) returns
0
“welcome to Java”.indexOf(“come”)
return 3
lastIndexOf return the index of the
character last time appear in string
Converting characters and
numeric values to strings
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The valueOf method can be used to convert
an array of characters into a string.
There are several overloaded versions of
the valueOf method that can be used to
convert a character and numeric values to
strings with different parameter type
For example, to convert a double value 5.44
to a string,
String.valueOf(5.44)
Character class
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Java provide a wrapper class for every data
type.
Character for char
You can create a Character object from a
char value
Character ch = new Character(‘a’);
charValue() method return the character
value wrapped in the Character object.
See page 268 Chapter 7.3 for the full list of
methods in Character class