Searching
Strings
The String class provides two methods that allow you to search a string
for a specified character or substring:
indexOf( ) Searches for the first occurrence of a
character or substring.
lastIndexOf( ) Searches for the last occurrence of a
character or substring.
These two methods are
overloaded in several different ways. In all cases, the methods return the
index at which the character or substring was found, or –1 on failure.
To search for the first
occurrence of a character, use int indexOf(int ch)
To search for the last
occurrence of a character, use int lastIndexOf(int ch)
Here, ch is the character being sought.
To search for the first or
last occurrence of a substring, use
int indexOf(String str) int lastIndexOf(String str)
Here, str specifies the substring.
You can specify a starting
point for the search using these forms:
int indexOf(int ch, int startIndex) int lastIndexOf(int ch,
int startIndex)
int indexOf(String str, int startIndex) int lastIndexOf(String str, int startIndex)
Here, startIndex specifies the index at which point the search begins.
For indexOf( ), the search runs from
startIndex to the end of the string.
For lastIndexOf( ), the search runs
from startIndex to zero.
The following example shows
how to use the various index methods to search inside of a String:
// Demonstrate indexOf() and lastIndexOf().
class indexOfDemo {
public static void main(String args[]) {
String s = "Now is the time for all good
men " + "to come to the aid of their country.";
System.out.println(s); System.out.println("indexOf(t)
= " +
s.indexOf('t'));
System.out.println("lastIndexOf(t) = " +
s.lastIndexOf('t'));
System.out.println("indexOf(the) = " +
s.indexOf("the"));
System.out.println("lastIndexOf(the) = " +
s.lastIndexOf("the"));
System.out.println("indexOf(t, 10) = " +
s.indexOf('t', 10));
System.out.println("lastIndexOf(t, 60) = " +
s.lastIndexOf('t', 60));
System.out.println("indexOf(the, 10) = " +
s.indexOf("the", 10));
System.out.println("lastIndexOf(the, 60) = " +
s.lastIndexOf("the", 60));
}
}
To search for the last
occurrence of a character, use int lastIndexOf(int ch)
Here, ch is the character being sought.
To search for the first or
last occurrence of a substring, use
int indexOf(String str) int lastIndexOf(String str)
Here, str specifies the substring.
You can specify a starting
point for the search using these forms:
int indexOf(int ch, int startIndex) int lastIndexOf(int ch,
int startIndex)
int indexOf(String str, int startIndex) int lastIndexOf(String str, int startIndex)
Here, startIndex specifies the index at which point the search begins.
For indexOf( ), the search runs from
startIndex to the end of the string.
For lastIndexOf( ), the search runs
from startIndex to zero.
The following example shows
how to use the various index methods to search inside of a String:
// Demonstrate indexOf() and lastIndexOf().
class indexOfDemo {
public static void main(String args[]) {
String s = "Now is the time for all good
men " + "to come to the aid of their country.";
System.out.println(s);
System.out.println("indexOf(t) = " +
s.indexOf('t'));
System.out.println("lastIndexOf(t) = " +
s.lastIndexOf('t'));
System.out.println("indexOf(the) = " +
s.indexOf("the"));
System.out.println("lastIndexOf(the) = " +
s.lastIndexOf("the")); System.out.println("indexOf(t,
10) = " +
s.indexOf('t', 10));
System.out.println("lastIndexOf(t, 60) = " +
s.lastIndexOf('t', 60));
System.out.println("indexOf(the, 10) = " +
s.indexOf("the", 10));
System.out.println("lastIndexOf(the, 60) = " +
s.lastIndexOf("the", 60));
}
}
Here is the output of this
program:
Now is the time for all good men to come to the
aid of their country. indexOf(t) = 7
lastIndexOf(t) = 65
indexOf(the) = 7
lastIndexOf(the) = 55
indexOf(t, 10) = 11
lastIndexOf(t, 60) = 55
indexOf(the, 10) = 44
lastIndexOf(the, 60) = 55
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