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Lesson 4 - Simple I/O
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String Objects page 6 of 10

  1. Next to numbers, strings are the most important data type that most programs use. A string is a sequence of characters such as "Hello". In Java, strings are enclosed in quotation marks, which are not themselves part of the string

  2. String objects can be constructed in two ways:

    String name = "Bob Binary";
    String anotherName = new String("Betty Binary");

    Due to the usefulness and frequency of use of Strings, a shorter version without the keyword new, was developed as a short-cut way of creating a String object. This creates a String object containing the characters between quote marks, just as before. A String created in this method is called a Stringliteral. Only Strings have a short-cut like this. All other objects are constructed by using the new operator.

  3. Assignment can be used to place a reference to adifferent String into the variable.

    name = "Boris";
    anotherName = new String("Bessy");
  4. The number of characters in a String is called the length of the string. For example, the length of "Hello World!" is 12. You can compute the length of a String with the length method.

    int n = name.length();

    Unlike numbers, Strings are objects. Therefore, you can call methods on strings. In the above example, the length of the String object name is computed with the method call name.length().

  5. A String of length zero, containing no characters, is called the empty string and is written as "". For example:

    String empty = "";
  6. Programmers often make one String object from two strings with the + operator, which concatenates (connects) two or more strings into one string. Concatenation and these string messages are illustrated below.

    public class DemoStringMethods
    {
      public static void main(String[] args)
      {
        String a = new String("Any old");
        String b = " String";
        String aString = a + b; // aString is "Any old String"
        
        // Show string a
        System.out.println("a: " + a);
    
        // Show string b
        System.out.println("b: " + b);
    
        // Show the result of concatenating a and b
        System.out.println("a + b: " + aString);
    
        // Show the number of characters in the string
        System.out.println("length: " + aString.length());
      }
    }
    
    Run output:
    
    a: Any old
    b:  String
    a + b: Any old String
    length: 14
  7. Notice that using strings in the context of input and output statements is identical to using other data types.

  8. The String class will be covered in depth in a later lesson. For now you will use strings for simple input and output in programs.


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