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javaregexvalidationnotnull

Why does Java java.util.regex Pattern Matcher Throw Runtime Exceptions?

The following code throw a runtime exception in my project

Pattern pattern = Pattern.compile("");
Matcher matcher = pattern.matcher(null);

Uncaught exception: java.lang.NullPointerException: Cannot invoke "java.lang.CharSequence.length()" because "this.text" is null at java.base/java.util.regex.Matcher.getTextLength(Matcher.java:1769) at java.base/java.util.regex.Matcher.reset(Matcher.java:415) at java.base/java.util.regex.Matcher.(Matcher.java:252) at java.base/java.util.regex.Pattern.matcher(Pattern.java:1134)

In my IDE it says this method is marked @NotNull (see below) which is I assume why it's throwing an exception because my understanding is that if there's a "NotNull validator" on my Classpath it will do this.

My questions are:

  1. Where is the @NotNull annotation even coming from? I don't see it in the JavaDoc - is that actually part of the Java SDK?
  2. How do I know what validator is throwing that exception?
  3. If it's not the validator then why is is throwing an Exception that's not mentioned in the method signature?

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Solution

    1. @NotNull is a Code-Contract Annotation added by IntelliJ.

    2. The annotation (or its potential validator) is not the one throwing the exception, it only hints you about potential issues at design-time but the code still compiles. Instead, Matcher.getTextLength() is throwing the exception at runtime, as shown in the stack trace.

    3. The exception being thrown is a NullPointerException, subclass of RuntimeException which do not need to be declared in the methods' signatures, in contrary to so-called checked exceptions (it would be pretty verbose to specify each time a NullPointerException can be thrown, although it may still be interesting to make it explicit in some cases).