Java Problem Solving for Beginners (with solutions)

How to Replace the String Between Two Characters in Java 📌[All Method]️

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Replacing specific characters in a string is quite easy in Java (using replace()), but how can we replace an entire substring between two characters?

Suppose we have a string that is meant to represent a URL path.

String url = "/path/{id}/resource";

Let’s say we want to replace the string between the opening and closing curly braces {} with an asterisk *.

String updatedUrl = "/path/*/resource";

Using replaceAll()

We can do this using replaceAll().

The first parameter takes in a regular expression while the second takes in a string with the replacement value.

String start = "\\{";
String end = "\\}";
String updatedUrl = url.replaceAll(start + ".*" + end, "*");

Our start and end symbols need to be escaped if they are special characters used in regular expressions.

In Java, these characters will need to be escaped: \.[]{}()<>*+-=!?^$|.

In order to escape a special character, we can add the a single backslash \, or the escape character, before the special character.

However, we also need to escape that backslash with the escape character (hint: another backslash), since it too is a special character.

This is why we will often see double backslashes \\ in regular expressions.

This string \\{.*\\} translates to the sequence \{.*\}, which literally matches our url against {.*}.

Greediness

While this is a great start to using regular expressions in our replaceAll() method, we’ll have to deal with the greediness of our matching.

This relates to the .* portion of the regular expression.

Greedy Reluctant Possessive Meaning
X? X?? X?+ X, once or not at all
X* X*? X*+ X, zero or more times
X+ X+? X++ X, one or more times
X{n} X{n}? X{n}+ X, exactly n times
X{n,} X{n,}? X{n,}+ X, at least n times
X{n,m} X{n,m}? X{n,m}+ X, at least n but not more than m times

Based on our use case, we can vary our greedy quantifiers to match as little or as much as we need.


Revise the code and make it more robust with proper test case and check an error there before implementing into a production environment.
If you need assistance at any stage, please feel free to contact me.

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