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The String Literal

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A String literal is a sequence of characters used by Java programmers to populate String objects or display text to a user. The characters could be letters, numbers or symbols and are enclosed within two quotation marks. For example,

"I live at 22b Baker Street!"

is a String literal.

Although in your Java code you will be writing the text within the quotes, the Java compiler will interpreting the characters as Unicode code points.

Unicode is a standard that assigns all letters, numbers and symbols a unique numerical code. This means that every computer will display the same character for each numerical code. This means that if you know the number values you can actually write String literals using Unicode values:

"\u0049\u0020\u006C\u0069\u0076\u0065\u0020\u0061\u0074\u0020\u0032\u0032\u0042\u0020\u0042\u0061\u006B\u0065\u0072\u0020\u0053\u0074\u0072\u0065\u0065\u0074\u0021"

represents the same String value as "I live at 22b Baker Street!" but obviously it's not as nice to write!

Unicode and normal text characters can also be mixed. This is useful for characters you might not know how to type. For example, a character with an umlaut (e.g., Ä, Ö) as in "Thomas Müller plays for Germany." would be:

"Thomas M\u00FCller plays for Germany."

To assign a String object a value just use a String literal:

String text = "So does Dr Watson";

Escape Sequences

There are certain characters that you might want to include into a String literal which need to be identified to the compiler. Otherwise it might get confused and not know what the String value is supposed to be. For example, imagine you want to put a quotation mark within a String literal:

"So my friend said, "It's how big?""

This would confuse the compiler because it expects all String literals to begin and end with a quotation mark. To get around this we can use what is known as an escape sequence - these are characters which are preceded by a backslash (in fact you've already seen several if you look back at the Unicode character codes). For example, a quotation mark has the escape sequence:

\"

So the String literal above would be written:

"So my friend said, \"It's how big?\""

Now the compiler will come to the backslash and know the quotation mark is part of the String literal instead of its end point. If you're thinking ahead you're probably wondering but what if I want to have a backslash in my String literal? Well, that's easy - its escape sequence follows the same pattern - a backslash before the character:

\\

Some of the escape sequences available don't actually print a character to the screen. There are times when you might want to have display some text split by a newline. For example:

The first line.
The second line.

This can be done by using the escape sequence for the newline character:

"The first line.\nThe second line."

It's a useful way to put a little bit of formatting into one Sting literal.

There are several useful escape sequences worth knowing:

  • \t is for inserting tabs into the literal
  • \b inserts a backspace
  • \n inserts a newline
  • \r inserts a carriage return
  • \' inserts a single quotation mark
  • \" inserts a double quotation mark
  • \\ inserts a backslash

Example Java code can be found in the Fun With Strings Example Code.

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