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));
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:
Example
int x = 10;
int y = 20;
int z = x + y; // z will be 30 (an integer/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:
Example
String x = "10";
int y = 20;
String z = x + y; // z will be 1020 (a String)
Strings - 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:
Example
String txt = "We are the so-called \"Vikings\" from the north.";
The sequence \' inserts a single quote in a string:
Example
String txt = "It\'s alright.";
The sequence \\ inserts a single backslash in a string:
Example
String txt = "The character \\ is called backslash.";
Other common escape sequences that are valid in Java are:
| Code | Result |
|---|---|
| \n | New Line |
| \r | Carriage Return |
| \t | Tab |
| \b | Backspace |
| \f | Form Feed |