Strings are used for storing text.
String variable contains a collection of characters surrounded by double quotes:
Create a variable of type
String and assign it a value:
String greeting = "Hello";
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
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
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
indexOf() method returns the index (the position) of the first occurrence of a specified text in a string (including whitespace):
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 …
+ operator can be used between strings to combine them. This is called concatenation:
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:
String firstName = "John "; String lastName = "Doe"; System.out.println(firstName.concat(lastName));
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:
\" inserts a double quote in a string:
String txt = "We are the so-called \"Vikings\" from the north.";
\' inserts a single quote in a string:
String txt = "It\'s alright.";
\\ inserts a single backslash in a string:
String txt = "The character \\ is called backslash.";
Six other escape sequences are valid in Java:
Adding Numbers and Strings
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:
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:
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:
String x = "10"; int y = 20; String z = x + y; // z will be 1020 (a String)