Java Strings
Java Strings
Strings are used for storing text.
A String variable contains a collection of characters surrounded by double quotes:
Example
Create a variable of type String and assign it a value:
String greeting = "Hello";
String Length
A String in Java is actually an object, which contain methods that can perform certain operations on strings. For example, the length of a string can be found with the length() method:
Example
String txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
System.out.println("The length of the txt string is: " + txt.length());
More String Methods
There are many string methods available, for example toUpperCase() and toLowerCase():
Example
String txt = "Hello World";
System.out.println(txt.toUpperCase()); // Outputs "HELLO WORLD"
System.out.println(txt.toLowerCase()); // Outputs "hello world"
Finding a Character in a String
The indexOf() method returns the index (the position)
of the first occurrence of a specified text in a string
(including whitespace):
Example
String txt = "Please locate where 'locate' occurs!";
System.out.println(txt.indexOf("locate")); // Outputs 7
Java counts positions from zero.
0 is the first position in a
string, 1 is the second, 2 is the third ...
String Concatenation
The + operator can be used between strings to
combine them. This is called concatenation:
Example
String firstName = "John";
String lastName = "Doe";
System.out.println(firstName + " " + lastName);
Note that we have added an empty text (" ") to create a space between firstName and lastName on print.
You can also use the concat() method to concatenate two strings:
Example
String firstName = "John ";
String lastName = "Doe";
System.out.println(firstName.concat(lastName));
Special Characters
Because strings must be written within quotes, Java will misunderstand this string, and generate an error:
String txt = "We are the so-called "Vikings" from the north.";
The solution to avoid this problem, is to use the backslash escape character.
The backslash (\) escape character turns special characters into string characters:
| Escape character | Result | Description |
|---|---|---|
| \' | ' | Single quote |
| \" | " | Double quote |
| \\ | \ | Backslash |
The sequence \" inserts a double quote in a string:
The sequence \' inserts a single quote in a string:
The sequence \\ inserts a single backslash in a string:
Six other escape sequences are valid in Java:
| Code | Result | Try it |
|---|---|---|
| \n | New Line | Try it » |
| \r | Carriage Return | Try it » |
| \t | Tab | Try it » |
| \b | Backspace | Try it » |
| \f | Form Feed |
Adding Numbers and Strings
WARNING!
Java uses the + operator for both addition and concatenation.
Numbers are added. Strings are concatenated.
If you add two numbers, the result will be a number:
If you add two strings, the result will be a string concatenation:
Example
String x = "10";
String y = "20";
String z = x + y; // z will be 1020 (a String)
If you add a number and a string, the result will be a string concatenation:
Complete String Reference
For a complete reference of String methods, go to our Java String Methods Reference.
The reference contains descriptions and examples of all string methods.
Strings in Java are objects, and an object in Java is declared with the new keyword. However, instead of using the new keyword, you can easily just write the string text inside double quotes. This is called a "String literal". It is up to you which method you would like to use.
You will learn more about objects in a later chapter.
