Objektorienteeritud programmeerimine (Narva Kolledž) 2018/19 kevad

Session 4

Methods of class String

We had our first view of strings in the first session (see here): a string is any sequence of characters – letters, digits, spaces, punctuation, and other “special characters” placed between quotes.

In this section, we are going to have a closer look at methods applicable to strings:

To create a String object, we can use one of the String constructors whose argument is an array of chars (each char is written between single quotes!):

char[] arrayOfChars = {'G','o','o','d',' ','m','o','r','n','i','n','g'};
String message = new String(arrayOfChars);
System.out.println(message);

An instance of String class can be created in a simpler way:

String message = "Good morning";

Once we have an instance of String data type, we can use methods of its class:

public class HelloString {
    public static void main(String[] args) {

        String myString = "Mart Mardikas";

        System.out.println("String length: " + myString.length()); // 13
        System.out.println(myString.startsWith("Mart")); // true
        System.out.println(myString.endsWith("kas")); // true
        System.out.println(myString.endsWith("Mart")); // false
        System.out.println("Index of the first 'a': " +
                           myString.indexOf('a')); // 1

        int rIndex = myString.indexOf('r');
        System.out.println("Index of the first 'r': " + rIndex); // 2
        System.out.println("Index of the next 'r': " +
                           myString.indexOf('r', rIndex + 1)); // 7

        int aIndex = myString.lastIndexOf('a');
        System.out.println("Index of the last 'a': " + aIndex); // 11
        System.out.println("Index of the Substring \\"Mardi\\": " +
                           myString.indexOf("Mardi")); // 5
        System.out.println("The 4th letter: "+myString.charAt(3)); // 't'

        //Compare two strings
        System.out.println(myString.equals("Mart Mardikas")); // true
        System.out.println(myString.equals("mart mardikas")); // false

        //Compare two strings ignoring case sensitivity
        System.out.println(myString.equalsIgnoreCase("mart mardikas"));  // true

        //Lexicographical comparison
        System.out.println(myString.compareTo("Jaan Jaaniste")); // >0
        System.out.println(myString.compareTo("Peeter Paan")); // <0
        System.out.println(myString.compareTo("Mart Mardikas")); // =0

        System.out.println(myString.replace('M', 'P')); // "Part Pardikas"
        System.out.println(myString.toUpperCase()); // "MART MARDIKAS"

        //String with spaces and new lines removed at the beginning and end of the string
        String yourString = " Mart \n";
        System.out.println(yourString.trim()); // "Mart"

        //Split the string near "ar"
        String[] stringParts = myString.split("ar");
        for (int i = 0; i<stringParts.length; i++){
            System.out.println(stringParts[i]);  // { "M", "t M", "dikas" }
        }
    }
}

Session 4