Add NullWriter.INSTANCE and deprecate NULL_WRITER.

Author: Gary Gregory

src/changes/changes.xml

@@ -93,6 +93,9 @@ The <action> type attribute can be add,update,fix,remove.
       <action dev="ggregory" type="add" due-to="Gary Gregory">
         Add NullPrintStream.INSTANCE and deprecate NULL_PRINT_STREAM.
       </action>
+      <action dev="ggregory" type="add" due-to="Gary Gregory">
+        Add NullWriter.INSTANCE and deprecate NULL_WRITER.
+      </action>
       <!-- UPDATE -->
       <action dev="ggregory" type="update" due-to="Dependabot">
         Bump Maven Javadoc plugin from 3.2.0 to 3.3.0.

src/main/java/org/apache/commons/io/output/NullWriter.java

@@ -27,9 +27,19 @@
 public class NullWriter extends Writer {
 
     /**
-     * A singleton.
+     * The singleton instance.
+     *
+     * @since 2.12.0
      */
-    public static final NullWriter NULL_WRITER = new NullWriter();
+    public static final NullWriter INSTANCE = new NullWriter();
+
+    /**
+     * The singleton instance.
+     *
+     * @deprecated Use {@link #INSTANCE}.
+     */
+    @Deprecated
+    public static final NullWriter NULL_WRITER = INSTANCE;
 
     /**
      * Constructs a new NullWriter.

src/test/java/org/apache/commons/io/output/NullWriterTest.java

@@ -27,7 +27,7 @@ public class NullWriterTest {
     @Test
     public void testNull() {
         final char[] chars = { 'A', 'B', 'C' };
-        try (final NullWriter writer = NullWriter.NULL_WRITER) {
+        try (final NullWriter writer = NullWriter.INSTANCE) {
             writer.write(1);
             writer.write(chars);
             writer.write(chars, 1, 1);

src/test/java/org/apache/commons/io/output/ProxyWriterTest.java

@@ -107,23 +107,23 @@ public void writeCharArrayPartial() throws Exception {
 
     @Test
     public void nullString() throws Exception {
-        try (final ProxyWriter proxy = new ProxyWriter(NullWriter.NULL_WRITER)) {
+        try (final ProxyWriter proxy = new ProxyWriter(NullWriter.INSTANCE)) {
             proxy.write((String) null);
             proxy.write((String) null, 0, 0);
         }
     }
 
     @Test
     public void nullCharArray() throws Exception {
-        try (final ProxyWriter proxy = new ProxyWriter(NullWriter.NULL_WRITER)) {
+        try (final ProxyWriter proxy = new ProxyWriter(NullWriter.INSTANCE)) {
             proxy.write((char[]) null);
             proxy.write((char[]) null, 0, 0);
         }
     }
 
     @Test
     public void nullCharSequence() throws Exception {
-        try (final ProxyWriter proxy = new ProxyWriter(NullWriter.NULL_WRITER)) {
+        try (final ProxyWriter proxy = new ProxyWriter(NullWriter.INSTANCE)) {
             proxy.append(null);
         }
     }

src/test/java/org/apache/commons/io/test/ThrowOnCloseWriter.java

@@ -31,7 +31,7 @@ public class ThrowOnCloseWriter extends ProxyWriter {
      * Default ctor.
      */
     public ThrowOnCloseWriter() {
-        super(NullWriter.NULL_WRITER);
+        super(NullWriter.INSTANCE);
     }
 
     /**