To match specific percentage patterns using Java regular expressions, you can use the following steps:

1. Import the necessary Java classes:

   import java.util.regex.Matcher;
   import java.util.regex.Pattern;
   

2. Define the regular expression pattern using the Pattern class:

   String regex = "\\d+(\\.\\d+)?%"; // Match one or more digits, an optional decimal part, and a percentage symbol
   Pattern pattern = Pattern.compile(regex);
   

3. Create a Matcher object to search for the pattern within a string:

   String input = "The discount is 25.5% and the tax rate is 7.8%.";
   Matcher matcher = pattern.matcher(input);
   

4. Use the find() method to find all occurrences of the pattern within the input string, and retrieve the matched values:

   while (matcher.find()) {
       String match = matcher.group(); // Get the matched percentage pattern
       System.out.println(match);
   }
   

In the above example, we define a regular expression pattern \\d+(\\.\\d+)?% to match percentage patterns. This pattern looks for one or more digits, an optional decimal part (denoted by \\.\\d+), and a percentage symbol (%).

We then create a Matcher object and search for the pattern within the input string. The find() method is used in a loop to find all occurrences of the pattern. The matched percentage pattern is retrieved using the group() method and printed.

By using regular expressions in Java, you can easily match specific percentage patterns or any other pattern you require for your application. Remember to consider any variations in the pattern you need to account for, such as decimal places or negative numbers.