Java中的“转义序列”的目的是什么？

Question

if I print ' (single quote) in the System.out.println() I can get exact output.

Like :

System.out.println("test'test");
output:  test'test

What is the purpose of using \\' escape sequence in java?

This also gives me the same output.

 System.out.println("test\'test");
 output:  test'test

pls explain what is the main purpose of \\' escape sequence in java

Answer 1

It's for use in character literals:

char c = '\'';

Without that, it would be painful to get a single apostrophe as a char .

Answer 2

This is useful for character literals stored in char .

Imagine you want a character constant to just hold a ' . You could do:

public static final char SINGLE_QUOTE = '';

This won't work as it only is an empty character, but we want a single quote. Hence the escape character \\' .

public static final char SINGLE_QUOTE = '\'';

If you print it on System.out.println , you'll see the difference.

For an exercise, try and take your exact example and see if you can print a double quote literal " without escaping it. You'll see it's not possible. You will have to escape it with \\" .

Reference: String literals and Escape Sequences for Character and String Literals .