1 files changed, 72 insertions, 0 deletions
diff --git a/junit4/src/main/java/junit/framework/ComparisonCompactor.java b/junit4/src/main/java/junit/framework/ComparisonCompactor.java
new file mode 100644
index 0000000..bbc3ba1
--- /dev/null
+++ b/junit4/src/main/java/junit/framework/ComparisonCompactor.java
@@ -0,0 +1,72 @@
+package junit.framework;
+
+public class ComparisonCompactor {
+
+	private static final String ELLIPSIS= "...";
+	private static final String DELTA_END= "]";
+	private static final String DELTA_START= "[";
+	
+	private int fContextLength;
+	private String fExpected;
+	private String fActual;
+	private int fPrefix;
+	private int fSuffix;
+
+	public ComparisonCompactor(int contextLength, String expected, String actual) {
+		fContextLength= contextLength;
+		fExpected= expected;
+		fActual= actual;
+	}
+
+	public String compact(String message) {
+		if (fExpected == null || fActual == null || areStringsEqual())
+			return Assert.format(message, fExpected, fActual);
+
+		findCommonPrefix();
+		findCommonSuffix();
+		String expected= compactString(fExpected);
+		String actual= compactString(fActual);
+		return Assert.format(message, expected, actual);
+	}
+
+	private String compactString(String source) {
+		String result= DELTA_START + source.substring(fPrefix, source.length() - fSuffix + 1) + DELTA_END;
+		if (fPrefix > 0)
+			result= computeCommonPrefix() + result;
+		if (fSuffix > 0)
+			result= result + computeCommonSuffix();
+		return result;
+	}
+
+	private void findCommonPrefix() {
+		fPrefix= 0;
+		int end= Math.min(fExpected.length(), fActual.length());
+		for (; fPrefix < end; fPrefix++) {
+			if (fExpected.charAt(fPrefix) != fActual.charAt(fPrefix))
+				break;
+		}
+	}
+
+	private void findCommonSuffix() {
+		int expectedSuffix= fExpected.length() - 1;
+		int actualSuffix= fActual.length() - 1;
+		for (; actualSuffix >= fPrefix && expectedSuffix >= fPrefix; actualSuffix--, expectedSuffix--) {
+			if (fExpected.charAt(expectedSuffix) != fActual.charAt(actualSuffix))
+				break;
+		}
+		fSuffix=  fExpected.length() - expectedSuffix;
+	}
+
+	private String computeCommonPrefix() {
+		return (fPrefix > fContextLength ? ELLIPSIS : "") + fExpected.substring(Math.max(0, fPrefix - fContextLength), fPrefix);
+	}
+
+	private String computeCommonSuffix() {
+		int end= Math.min(fExpected.length() - fSuffix + 1 + fContextLength, fExpected.length());
+		return fExpected.substring(fExpected.length() - fSuffix + 1, end) + (fExpected.length() - fSuffix + 1 < fExpected.length() - fContextLength ? ELLIPSIS : "");
+	}
+
+	private boolean areStringsEqual() {
+		return fExpected.equals(fActual);
+	}
+}