Practical Coding in Java

//
// HelloStrings.java
//


public class HelloStrings
{
    public static void main(String[] args)
    {
        String hello = "HelloWorld";

        // The + operator concatenates Strings

        System.out.println("hello: " + hello);

        // A String variable is a reference to a String object,
        // which has methods (functions) like `length()`

        System.out.println("hello.length(): " + hello.length());
        System.out.println();

        // String indexing is 0-based

        System.out.println("hello.charAt(0): " + hello.charAt(0));
        System.out.println("hello.charAt(1): " + hello.charAt(1));
        System.out.println("hello.charAt(2): " + hello.charAt(2));
        System.out.println();

        // The String method `substring(a,b)` returns the substring
        // specified by the half-open interval [a,b)

        String firstPart = hello.substring(0,5); 
        System.out.println("firstPart: " + firstPart);

        // substring(a) is shorthand for substring(a, length())

        String secondPart = hello.substring(5);
        System.out.println("secondPart: " + secondPart);
        System.out.println();

        // Use the equals() method to compare String values.  
        //
        // In the code below, s and t refer to the same String
        // object, i.e. s == t.  
        //
        // u is a different String object with the same value
        // "Hello", so s != u, but s.equals(u) == true.

        String s = new String("Hello"); 
        String t = s;                   
        String u = new String("Hello"); 

        System.out.println("s == t: " + (s == t));
        System.out.println("s == u: " + (s == u));
        System.out.println("s.equals(u): " +  s.equals(u));
    }
}