Java Strings

Strings are a series of characters. They can be single words, multiple words, or special characters. All strings are written out between double quotes.

Declaring Strings

String str = "hello";

In the example above, str is the name of the string and it has a value of "hello". Remember to capitalize String, as it is a class, rather than a primitive data type.

String Concatenations

When you are adding two strings together, you are concatenating them. The + ( plus ) operator combines two strings.

String str1 = "hello";
String str2 = "world";
System.out.println(str1 + str2);
// returns "helloworld"

String Index Numbers

The characters in a string are identified by index numbers. Index numbers start counting at 0.

H	E	L	L	O
0	1	2	3	4

Useful String Methods

Method	Returns
startsWith("a")	String
endsWith(“a”)	Boolean
length()	int: the length of the string ( number of characters )
indexOf(“a”)	int: the index of the first position where “a” is located
replace(“a”, “b”)	String
toUpperCase()	String
toLowerCase()	String
trim()	String

Strings are immutable, which means once we initialize them, their value cannot be changed. All methods that modify a string (like toUpperCase) return a new string object. The original string remains unaffected.

For reference:

https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/String.html