Package org.hamcrest

Interface Matcher<T>

Type Parameters:
T - the matched value type
All Superinterfaces:
SelfDescribing
All Known Implementing Classes:
AllOf, AnyOf, ArrayAsIterableMatcher, BaseMatcher, BigDecimalCloseTo, CharSequenceLength, CombinableMatcher, CustomMatcher, CustomTypeSafeMatcher, DescribedAs, DiagnosingMatcher, Every, FeatureMatcher, HasEqualValues, HasItemInArray, HasProperty, HasPropertyWithValue, HasToString, HasXPath, Is, IsAnything, IsArray, IsArrayContainingInAnyOrder, IsArrayContainingInOrder, IsArrayWithSize, IsBlankString, IsCloseTo, IsCollectionContaining, IsCollectionWithSize, IsCompatibleType, IsEmptyCollection, IsEmptyIterable, IsEmptyString, IsEqual, IsEqualCompressingWhiteSpace, IsEqualIgnoringCase, IsEventFrom, IsIn, IsInstanceOf, IsIterableContaining, IsIterableContainingInAnyOrder, IsIterableContainingInOrder, IsIterableContainingInRelativeOrder, IsIterableWithSize, IsMapContaining, IsMapWithSize, IsNaN, IsNot, IsNull, IsSame, MatchesPattern, SamePropertyValuesAs, StringContains, StringContainsInOrder, StringEndsWith, StringRegularExpression, StringStartsWith, SubstringMatcher, TypeSafeDiagnosingMatcher, TypeSafeMatcher
public interface Matcher<T> extends SelfDescribing

A matcher over acceptable values. A matcher is able to describe itself to give feedback when it fails.

Matcher implementations should NOT directly implement this interface. Instead, extend the BaseMatcher abstract class, which will ensure that the Matcher API can grow to support new features and remain compatible with all Matcher implementations.

When using Hamcrest, there is no guarantee as to how often matches() or describeMismatch() will be called, so the objects passed as actual arguments should not change when referenced. If you're testing a stream, a good practice is to collect the contents of the stream before matching.

N.B. Well designed matchers should be immutable.

See Also:

  • Method Details

    • matches

      boolean matches(Object actual)
      Evaluates the matcher for argument item. This method matches against Object, instead of the generic type T. This is because the caller of the Matcher does not know at runtime what the type is (because of type erasure with Java generics). It is down to the implementations to check the correct type.
      Parameters:
      actual - the object against which the matcher is evaluated.
      Returns:
      true if item matches, otherwise false.
      See Also:

    • describeMismatch

      void describeMismatch(Object actual, Description mismatchDescription)
      Generate a description of why the matcher has not accepted the item. The description will be part of a larger description of why a matching failed, so it should be concise. This method assumes that matches(item) is false, but will not check this.
      Parameters:
      actual - The item that the Matcher has rejected.
      mismatchDescription - The description to be built or appended to.

    • _dont_implement_Matcher___instead_extend_BaseMatcher_

      @Deprecated void _dont_implement_Matcher___instead_extend_BaseMatcher_()
      Deprecated.
      to make
      This method simply acts a friendly reminder not to implement Matcher directly and instead extend BaseMatcher. It's easy to ignore JavaDoc, but a bit harder to ignore compile errors .
      See Also: