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Finding substrings (with instance methods) in Strings

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• Finding the first occurence of a substring
  • The instance method used to find (locate) the first occurence of a substring sub in a string s is:

    s.indexOf( sub ) returns: the (integer) index (position) of the first occurence of the substring sub in string s -1 if substring sub is not found in string s

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    Examples:

    0123456789... "Hello World, Bye World".indexOf( "World" ) returns: 6 0123456789012345678901 "Hello World, Bye World".indexOf( "By" ) = 13 0123456789012345678901 "Hello World, Bye World".indexOf( "by" ) = -1

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• Finding the last occurence of a substring
  • The instance method used to find (locate) the last occurence of a substring sub in a string s is:

    s.lastIndexOf( sub ) returns: the (integer) index (position) of the last occurence of the substring sub in string s -1 if substring sub is not found in string s

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    Examples:

    0123456789012345678901 "Hello World, Bye World".lastIndexOf( "World" ) returns: 17

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    Java program that illustrates indexOf() and lastIndexOf():

    public class IndexOf1 { public static void main( String[] args ) { String s; int i; // 0123456789012345678901 s = "Hello World, Bye World"; i = s.indexOf( "World" ); System.out.println( " 0123456789012345678901"); System.out.println( "\"" + s + "\"" + ".indexOf( \"World\" ) = " + i ); i = s.indexOf( "By" ); System.out.println( " 0123456789012345678901"); System.out.println( "\"" + s + "\"" + ".indexOf( \"By\" ) = " + i ); i = s.indexOf( "by" ); System.out.println( " 0123456789012345678901"); System.out.println( "\"" + s + "\"" + ".indexOf( \"by\" ) = " + i ); /* ================================================= */ i = s.lastIndexOf( "World" ); System.out.println( " 0123456789012345678901"); System.out.println( "\"" + s + "\"" + ".lastIndexOf( \"World\" ) = " + i ); } }

    Output:

    0123456789012345678901 "Hello World, Bye World".indexOf( "World" ) = 6 0123456789012345678901 "Hello World, Bye World".indexOf( "By" ) = 13 0123456789012345678901 "Hello World, Bye World".indexOf( "by" ) = -1 0123456789012345678901 "Hello World, Bye World".lastIndexOf( "World" ) = 17

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   javac IndexOf1.java To run:          java IndexOf1