Add and use a package-private factory for UnsupportedOperationException
to provide exception messages with a consistent formatting.
diff --git a/src/main/java/org/apache/commons/io/LineIterator.java b/src/main/java/org/apache/commons/io/LineIterator.java
index 49c3a01..94f86e0 100644
--- a/src/main/java/org/apache/commons/io/LineIterator.java
+++ b/src/main/java/org/apache/commons/io/LineIterator.java
@@ -168,7 +168,7 @@ public void close() throws IOException {
      */
     @Override
     public void remove() {
-        throw new UnsupportedOperationException("Remove unsupported on LineIterator");
+        throw new UnsupportedOperationException("remove not supported");
     }
 
     //-----------------------------------------------------------------------
diff --git a/src/main/java/org/apache/commons/io/input/NullInputStream.java b/src/main/java/org/apache/commons/io/input/NullInputStream.java
index ce28f2c..f66f5cb 100644
--- a/src/main/java/org/apache/commons/io/input/NullInputStream.java
+++ b/src/main/java/org/apache/commons/io/input/NullInputStream.java
@@ -167,7 +167,7 @@ public void close() throws IOException {
     @Override
     public synchronized void mark(final int readlimit) {
         if (!markSupported) {
-            throw new UnsupportedOperationException("Mark not supported");
+            throw UnsupportedOperationExceptions.mark();
         }
         mark = position;
         this.readlimit = readlimit;
@@ -263,7 +263,7 @@ public int read(final byte[] bytes, final int offset, final int length) throws I
     @Override
     public synchronized void reset() throws IOException {
         if (!markSupported) {
-            throw new UnsupportedOperationException("Mark not supported");
+            throw UnsupportedOperationExceptions.reset();
         }
         if (mark < 0) {
             throw new IOException("No position has been marked");
diff --git a/src/main/java/org/apache/commons/io/input/NullReader.java b/src/main/java/org/apache/commons/io/input/NullReader.java
index b2cc429..82b4724 100644
--- a/src/main/java/org/apache/commons/io/input/NullReader.java
+++ b/src/main/java/org/apache/commons/io/input/NullReader.java
@@ -152,7 +152,7 @@ public void close() throws IOException {
     @Override
     public synchronized void mark(final int readlimit) {
         if (!markSupported) {
-            throw new UnsupportedOperationException("Mark not supported");
+            throw UnsupportedOperationExceptions.mark();
         }
         mark = position;
         this.readlimit = readlimit;
@@ -248,7 +248,7 @@ public int read(final char[] chars, final int offset, final int length) throws I
     @Override
     public synchronized void reset() throws IOException {
         if (!markSupported) {
-            throw new UnsupportedOperationException("Mark not supported");
+            throw UnsupportedOperationExceptions.reset();
         }
         if (mark < 0) {
             throw new IOException("No position has been marked");
diff --git a/src/main/java/org/apache/commons/io/input/SwappedDataInputStream.java b/src/main/java/org/apache/commons/io/input/SwappedDataInputStream.java
index d70ce92..86e0286 100644
--- a/src/main/java/org/apache/commons/io/input/SwappedDataInputStream.java
+++ b/src/main/java/org/apache/commons/io/input/SwappedDataInputStream.java
@@ -162,7 +162,7 @@ public int readInt() throws IOException, EOFException {
      */
     @Override
     public String readLine() throws IOException, EOFException {
-        throw new UnsupportedOperationException("Operation not supported: readLine()");
+        throw UnsupportedOperationExceptions.method("readLine");
     }
 
     /**
@@ -222,7 +222,7 @@ public int readUnsignedShort() throws IOException, EOFException {
      */
     @Override
     public String readUTF() throws IOException, EOFException {
-        throw new UnsupportedOperationException("Operation not supported: readUTF()");
+        throw UnsupportedOperationExceptions.method("readUTF");
     }
 
     /**
diff --git a/src/main/java/org/apache/commons/io/input/UnixLineEndingInputStream.java b/src/main/java/org/apache/commons/io/input/UnixLineEndingInputStream.java
index 42d72d4..e4bfe71 100644
--- a/src/main/java/org/apache/commons/io/input/UnixLineEndingInputStream.java
+++ b/src/main/java/org/apache/commons/io/input/UnixLineEndingInputStream.java
@@ -122,6 +122,6 @@ public void close() throws IOException {
      */
     @Override
     public synchronized void mark(final int readlimit) {
-        throw new UnsupportedOperationException("Mark not supported");
+        throw UnsupportedOperationExceptions.mark();
     }
 }
diff --git a/src/main/java/org/apache/commons/io/input/UnsupportedOperationExceptions.java b/src/main/java/org/apache/commons/io/input/UnsupportedOperationExceptions.java
new file mode 100644
index 0000000..acc213d
--- /dev/null
+++ b/src/main/java/org/apache/commons/io/input/UnsupportedOperationExceptions.java
@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.io.input;
+
+/**
+ * Package-private factory for {@link UnsupportedOperationException} to provide messages with consistent formatting.
+ *
+ * TODO Consider making this public and use from LineIterator.
+ */
+class UnsupportedOperationExceptions {
+
+    private static final String MARK_RESET = "mark/reset";
+
+    /**
+     * Creates a new instance of UnsupportedOperationException for a {@code mark} method.
+     *
+     * @return a new instance of UnsupportedOperationException
+     */
+    static UnsupportedOperationException mark() {
+        // Use the same message as in java.io.InputStream.reset() in OpenJDK 8.0.275-1.
+        return method(MARK_RESET);
+    }
+
+    /**
+     * Creates a new instance of UnsupportedOperationException for the given unsupported a {@code method} name.
+     *
+     * @param method A method name
+     * @return a new instance of UnsupportedOperationException
+     */
+    static UnsupportedOperationException method(final String method) {
+        return new UnsupportedOperationException(method + " not supported");
+    }
+
+    /**
+     * Creates a new instance of UnsupportedOperationException for a {@code reset} method.
+     *
+     * @return a new instance of UnsupportedOperationException
+     */
+    static UnsupportedOperationException reset() {
+        // Use the same message as in java.io.InputStream.reset() in OpenJDK 8.0.275-1.
+        return method(MARK_RESET);
+    }
+}
diff --git a/src/main/java/org/apache/commons/io/input/WindowsLineEndingInputStream.java b/src/main/java/org/apache/commons/io/input/WindowsLineEndingInputStream.java
index b557026..653ceab 100644
--- a/src/main/java/org/apache/commons/io/input/WindowsLineEndingInputStream.java
+++ b/src/main/java/org/apache/commons/io/input/WindowsLineEndingInputStream.java
@@ -130,6 +130,6 @@ public void close() throws IOException {
      */
     @Override
     public synchronized void mark(final int readlimit) {
-        throw new UnsupportedOperationException("Mark not supported");
+        throw UnsupportedOperationExceptions.mark();
     }
 }
diff --git a/src/test/java/org/apache/commons/io/input/NullInputStreamTest.java b/src/test/java/org/apache/commons/io/input/NullInputStreamTest.java
index b886024..4ad1d35 100644
--- a/src/test/java/org/apache/commons/io/input/NullInputStreamTest.java
+++ b/src/test/java/org/apache/commons/io/input/NullInputStreamTest.java
@@ -33,6 +33,9 @@
  */
 public class NullInputStreamTest {
 
+    // Use the same message as in java.io.InputStream.reset() in OpenJDK 8.0.275-1.
+    private static final String MARK_RESET_NOT_SUPPORTED = "mark/reset not supported";
+
     @Test
     public void testRead() throws Exception {
         final int size = 5;
@@ -178,14 +181,14 @@ public void testMarkNotSupported() throws Exception {
             input.mark(5);
             fail("mark() should throw UnsupportedOperationException");
         } catch (final UnsupportedOperationException e) {
-            assertEquals("Mark not supported", e.getMessage(), "mark() error message");
+            assertEquals(MARK_RESET_NOT_SUPPORTED, e.getMessage(), "mark() error message");
         }
 
         try {
             input.reset();
             fail("reset() should throw UnsupportedOperationException");
         } catch (final UnsupportedOperationException e) {
-            assertEquals("Mark not supported", e.getMessage(), "reset() error message");
+            assertEquals(MARK_RESET_NOT_SUPPORTED, e.getMessage(), "reset() error message");
         }
         input.close();
     }
diff --git a/src/test/java/org/apache/commons/io/input/NullReaderTest.java b/src/test/java/org/apache/commons/io/input/NullReaderTest.java
index 9782ef5..d1458f4 100644
--- a/src/test/java/org/apache/commons/io/input/NullReaderTest.java
+++ b/src/test/java/org/apache/commons/io/input/NullReaderTest.java
@@ -33,6 +33,9 @@
  */
 public class NullReaderTest {
 
+    // Use the same message as in java.io.InputStream.reset() in OpenJDK 8.0.275-1.
+    private static final String MARK_RESET_NOT_SUPPORTED = "mark/reset not supported";
+
     @Test
     public void testRead() throws Exception {
         final int size = 5;
@@ -175,14 +178,14 @@ public void testMarkNotSupported() throws Exception {
             reader.mark(5);
             fail("mark() should throw UnsupportedOperationException");
         } catch (final UnsupportedOperationException e) {
-            assertEquals("Mark not supported", e.getMessage(), "mark() error message");
+            assertEquals(MARK_RESET_NOT_SUPPORTED, e.getMessage(), "mark() error message");
         }
 
         try {
             reader.reset();
             fail("reset() should throw UnsupportedOperationException");
         } catch (final UnsupportedOperationException e) {
-            assertEquals("Mark not supported", e.getMessage(), "reset() error message");
+            assertEquals(MARK_RESET_NOT_SUPPORTED, e.getMessage(), "reset() error message");
         }
         reader.close();
     }