Section 2.6 Strings
The Java String type is used to represent a sequence of characters. Note that a String is not a Java primitive type like the type we’ve considered this far. Rather, as String is a more complex type called a class. While primitive types are just data stored in memory, class types, like Strings, are capable of more than just providing access to data in memory. Objects can include the ability to work on data itself. For example, a String can interrogate and manipulate its character data in numerous ways. You can ask a String for the number of characters it holds, to return a copy of itself with all upper case or all lower case letters, and whether or not the characters contains a smaller String, etc.
Strings are a special type in the Java language. Strings are the only non-literal Java type having its own literal notation. Strings may be created in Java simply by writing a sequence of zero or more characters surrounded by double-quotes (""). Compare this with the Java char literal, which is written as exactly one character surrounded with single-quotes (’’). The String literal notation is very useful because Strings are so common.
Creating a String in Java can be done in several ways. A common approach is to write a String literal, which are written as a character sequence enclosed in double quotation marks. In the following example, the String variable myString is declared and initialized with the character sequence Hello, world!.
String myString = "Hello, world!";
Strings in Java are immutable, which means that once a String is created, its value cannot be changed. Any operation that seems to modify a String actually creates a new String containing the modified value. For example, consider the following JShell session.
jshell> String original = "Hello"; // Creates a new String
original ==> "Hello"
| created variable original : String
jshell> String modified = original + ", world!"; // Creates a modified String
modified ==> "Hello, world!"
| created variable modified : String
jshell>
In the previous example, you’ll see that the
+ operator was used to "add" two Strings, one stored in the variable
original and the other written as a String literal surrounded by double-quotes. When operands of the
+ operator have type String, the
+ operator
concatenates the two String operands and returns a new String. By contrast, when operands of
+ are numbers, the two numeric operands are added together to produce the sum. This is a good example of how the behavior of an operator in Java can depend on the operand types. We will explore this further in the next section, and learn much more about Strings in the Section
The String Class.
Activity 2.6.1.
Declare a variable name of type String and initialize it with your own first name. Concatenate your last name to the variable and reassign the new String back to the original variable.
Answer.jshell> String name = "Roscoe";
name ==> "Roscoe"
| created variable name : String
jshell> name = name + " West";
name ==> "Roscoe West"
| assigned to name : String
jshell>
