package org.hamcrest.core;

import org.hamcrest.BaseMatcher;
import org.hamcrest.Description;
import org.hamcrest.Matcher;

import java.util.regex.Pattern;

import static java.lang.Integer.parseInt;

* Provides a custom description to another matcher.

public class DescribedAs<T> extends BaseMatcher<T> {
private final String descriptionTemplate;
private final Matcher<T> matcher;
private final Object[] values;

private final static Pattern ARG_PATTERN = Pattern.compile("%([0-9]+)");

public DescribedAs(String descriptionTemplate, Matcher<T> matcher, Object[] values) {
this.descriptionTemplate = descriptionTemplate;
this.matcher = matcher;
this.values = values.clone();

public boolean matches(Object o) {
return matcher.matches(o);

public void describeTo(Description description) {
java.util.regex.Matcher arg = ARG_PATTERN.matcher(descriptionTemplate);

int textStart = 0;
while (arg.find()) {
description.appendText(descriptionTemplate.substring(textStart, arg.start()));
textStart = arg.end();

if (textStart < descriptionTemplate.length()) {

public void describeMismatch(Object item, Description description) {
matcher.describeMismatch(item, description);

* Wraps an existing matcher, overriding its description with that specified.
All other functions are
* delegated to the decorated matcher, including its mismatch description.
* For example:
* <pre>describedAs("a big decimal equal to %0", equalTo(myBigDecimal), myBigDecimal.toPlainString())</pre>


* @param description
*the new description for the wrapped matcher
* @param matcher
*the matcher to wrap
* @param values
*optional values to insert into the tokenised description

public static <T> Matcher<T> describedAs(String description, Matcher<T> matcher, Object... values) {
return new DescribedAs<T>(description, matcher, values);