Strings - A Review

String examples

This example has most of what we need in strings. Go through it carefully.

import java.util.*;

public class StringReview {

    public static void main (String[] argv)
    {
        // Simple assignment using a constant.
        String str1 = "qwerty";
        System.out.println ("str1=" + str1);
        
        // Assignment using an instance of the class String.
        String str2 = new String ("qwerty");

        // Note use of concatenation operator and length() method in String.
        String str3 = "str2=" + str2 + " has length " + str2.length();
        System.out.println (str3);

        // Use the equals() method to determine string equality.
        boolean str1EqualsStr2 = str1.equals (str2);
        System.out.println ("str1 eq str2: " + str1EqualsStr2);
        
        // Beware of using ==
        String str4 = "qwerty";
        if (str1 == str4) {
            System.out.println ("This seems to work");
        }
        
        String str5 = new String ("qwert");
        String str6 = str5 + "y";
        if (str1 == str6) {
            System.out.println ("This seems to work");
        }
        else {
            // This is what gets printed.
            System.out.println ("Oops  - this didn't work");
        }
        
        if ( str1.equals(str6) ) {
            System.out.println ("This definitely works");
        }
        

        // Sometimes it's useful to ignore case.
        String str7 = "qWeRtY";
        if ( str1.equalsIgnoreCase(str7) ) {
            System.out.println ("This is useful");
        }
        

        // Some useful String functions.

        
        // Examine a char inside the string.
        char ch = str1.charAt (3);
        System.out.println ("Char at position 3 in String " + str1 + " is " + ch);
        // Prints 'r'

        // Extract a substring (without changing the original).
        String subStr = str1.substring (1, 3);
        System.out.println ("Chars from 1-3 in String " + str1 + ": " + subStr); 
        // Prints "we"
        
        // Locate first occurence of a char.
        int indexInString = str1.indexOf ('r');
        System.out.println ("Index of r in " + str1 + ": " + indexInString);  
        // index=3

        // Shortcut operator for concatenation.
        str1 += str2;
        System.out.println (str1);  
        // Prints "quertyqwerty"

        // Extract char's in an array.
        char[] letters = str1.toCharArray ();
        System.out.println ( "Char array: " + Arrays.toString(letters) );

        // Splitting by whitespace.
        String str8 = new String ("Jack and Jill went up the hill");
        String[] pieces = str8.split (" ");
        // Notice how to print the quote character in a string:
        System.out.println ("String \"" + str8 + "\" has " + pieces.length + " pieces:");
        for (int i=0; i<pieces.length; i++) {
            System.out.println (pieces[i]);
        }
        
        // Alphabetical-order comparison
        String str9 = "aardvark";
        String str10 = "Zygote";
        compare (str9, str10);             // Prints "Zygote precedes aardvark"
        compareLowercase (str9, str10);    // Prints "aardvark precedes zygote"
    }


    static void compare (String s1, String s2)
    {
        // Use the compareTo() method in the class String.
        // This returns -1 if alphabetically before, +1 if after, 0 if equal.
        if ( s1.compareTo(s2) < 0 ) {
            System.out.println (s1 + " precedes " + s2);
        }
        else if ( s1.compareTo(s2) > 0 ) {
            System.out.println (s2 + " precedes " + s1);
        }
        else {
            System.out.println (s2 + " equals " + s1);
        }
    }

    static void compareLowercase (String s1, String s2)
    {
        // Change to lowercase for case-free comparison.
        compare (s1.toLowerCase(), s2.toLowerCase());
    }
    

}