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What is a string?
A string is commonly considered to be a sequence of characters stored in memory and accessible as a unit.
Java implements strings using the String class and the StringBuffer class.
What is a string literal?
Java considers a series of characters surrounded by quotation marks as shown in Figure 7 to be a string literal.
| Figure 7 . A string literal. |
|---|
"This is a string literal in Java." |
This is just an introduction to strings
A major section of a future module will be devoted to the topic of strings, so this discussion will be brief.
String objects cannot be modified
String objects cannot be changed once they have been created. (They are said to be immutable.) If you have that need, use the StringBuffer class instead.
StringBuffer objects can be used to create and manipulate character data as the program executes.
Java supports string concatenation using the overloaded + operator as shown in Figure 8 .
| Figure 8 . String concatenation. |
|---|
"My variable has a value of " + myVar
+ " at this point in the program." |
Coercion of an operand to type String
The overloaded + operator is used to concatenate strings. If either operand is type String , the other operand is coerced into type String and the two strings are concatenated.
Therefore, in addition to concatenating the strings, Java also converts values of other types, such as myVar in Figure 8 , to character-string format in the process.
Declaring and instantiating a String array
The statement in Figure 9 declares and instantiates an array of references to five String objects.
| Figure 9 . Declaring and instantiating a String array. |
|---|
String[] myArrayOfStringReferences = new String[5]; |
No string data at this point
Note however, that this array doesn't contain the actual String objects. Rather, it simply sets aside memory for storage of five references of type String . (The array elements are automatically initialized to null.) No memory has been set aside to store the characters that make up the individual String objects. You must allocate the memory for the actual String objects separately using code similar to the code shown in Figure 10 .
| Figure 10 . Allocating memory to contain the String objects. |
|---|
myArrayOfStringReferences[0] = new String("This is the first string.");
myArrayOfStringReferences[1]= new String(
"This is the second string."); |
The new operator is not required for String class
Although it was used in Figure 10 , the new operator is not required to instantiate an object of type String . I will discuss the ability of Java to instantiate objects of type String without the requirement to use the new operator in a future module.
I encourage you to copy the code from Listing 1 , Listing 2 , and Listing 3 . Compile the code and execute it. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.
As you approach the end of this group of Programming Fundamentals modules, you should be preparing yourself for the more challenging ITSE 2321 OOPtracks identified below:
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
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