what is Java Strings, how to use String Length,finding character in string,java method,java classes,String Concatenation,Adding Numbers and Strings

Java Strings

Java Strings

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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";

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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());

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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"

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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:

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.";

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)