I'm trying to learn about Regular Expressions

Question

1.Based on this code https://docs.oracle.com/javase/tutorial/essential/regex/test_harness.html

Can anyone please explain what is this \"%s\" in

while (matcher.find()) {
        console.format("I found the text" + " \"%s\" starting at " +
        "index %d and ending at index %d.%n",
        matcher.group(),
        matcher.start(),
        matcher.end());
        found = true;
}

I just know that %s is for string.

2.Refering the meta-characters https://docs.oracle.com/javase/tutorial/essential/regex/literals.html is there any explanation for this outputs?

`%s` a formatter character and serves the purpose of format-based printing, which has nothing to do with regular expressions per se. API [here](https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html). — Mena, Jan 26 '18 at 14:50

Youcef LAIDANI · Accepted Answer · 2018-01-26T14:58:42.627

1

\"%s\" mean you want to put a String between two quotes for example the result can be :

I found the text "some string"
//""-------------^           ^
// %s             ^_________^

%s use for Strings, if you want to use digit you can use %d and so on

In Java quote should be escaped how? you can use backslash \" so consider I have a String which contain quotes like this Hello "World" how to use this as a String in Java :

String string = "Hello "World"";  //<<------- this is an error syntax

To solve it, you have to escape the quotes :

String string = "Hello \"World\"";
                       ^      ^

take a look at https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html

edited Jan 26 '18 at 14:58

answered Jan 26 '18 at 14:50

Youcef LAIDANI

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what are the two back slashes for? – Aashit Garodia Jan 26 '18 at 14:55
1

They escape the quotes (`"`). You can remove them and you'll see what error you get. – Jérôme Jan 26 '18 at 14:57
1

@Jérôme you will get `java.lang.RuntimeException: Uncompilable source code - not a statement` – Youcef LAIDANI Jan 26 '18 at 15:02
Thank you so much @YCF_L Can you suggest me some sites from where I can learn specific topics? – Aashit Garodia Jan 26 '18 at 15:15

Dumbo · Answer 2 · 2018-01-28T10:22:46.287

1

The percentage sign (%) in a String in combination with the letters b, c, d, e, f, s, is used to limit the number of characters to display.

%b- booleans
%c- character
%d- integer
%e- scientific notation
%f- floating point number (double, float)
%s- String

For example:

String text = "abcdef";
System.out.printf("%.3s", text); //output:  abc

or

String text = "\"abcdef\"";
System.out.printf("%.3s", text); //output:  "ab

edited Jan 28 '18 at 10:22

answered Jan 26 '18 at 15:02

Dumbo

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btw it is "%.3s" . Anyways Thanks. – Aashit Garodia Jan 26 '18 at 15:18

I'm trying to learn about Regular Expressions

2 Answers2