Refactor null-checks.

Author: Gary Gregory

src/main/java/org/apache/commons/io/filefilter/AbstractFileFilter.java

@@ -39,6 +39,13 @@
  */
 public abstract class AbstractFileFilter implements IOFileFilter, PathVisitor {
 
+    static <T> T requireNonNull(final T obj, final String message) {
+        if (obj == null) {
+            throw new IllegalArgumentException(message);
+        }
+        return obj;
+    }
+
     static FileVisitResult toDefaultFileVisitResult(final boolean accept) {
         return accept ? FileVisitResult.CONTINUE : FileVisitResult.TERMINATE;
     }

src/main/java/org/apache/commons/io/filefilter/DelegateFileFilter.java

@@ -39,26 +39,22 @@ public class DelegateFileFilter extends AbstractFileFilter implements Serializab
     /**
      * Constructs a delegate file filter around an existing FileFilter.
      *
-     * @param filter  the filter to decorate
+     * @param fileFilter  the filter to decorate
      */
-    public DelegateFileFilter(final FileFilter filter) {
-        if (filter == null) {
-            throw new IllegalArgumentException("The FileFilter must not be null");
-        }
-        this.fileFilter = filter;
+    public DelegateFileFilter(final FileFilter fileFilter) {
+        requireNonNull(fileFilter, "filter");
+        this.fileFilter = fileFilter;
         this.filenameFilter = null;
     }
 
     /**
      * Constructs a delegate file filter around an existing FilenameFilter.
      *
-     * @param filter  the filter to decorate
+     * @param filenameFilter  the filter to decorate
      */
-    public DelegateFileFilter(final FilenameFilter filter) {
-        if (filter == null) {
-            throw new IllegalArgumentException("The FilenameFilter must not be null");
-        }
-        this.filenameFilter = filter;
+    public DelegateFileFilter(final FilenameFilter filenameFilter) {
+        requireNonNull(filenameFilter, "filter");
+        this.filenameFilter = filenameFilter;
         this.fileFilter = null;
     }
 

src/main/java/org/apache/commons/io/filefilter/MagicNumberFileFilter.java

@@ -164,9 +164,7 @@ public MagicNumberFileFilter(final byte[] magicNumber) {
      *         is a negative number.
      */
     public MagicNumberFileFilter(final byte[] magicNumbers, final long offset) {
-        if (magicNumbers == null) {
-            throw new IllegalArgumentException("The magic number cannot be null");
-        }
+        requireNonNull(magicNumbers, "magicNumbers");
         if (magicNumbers.length == 0) {
             throw new IllegalArgumentException("The magic number must contain at least one byte");
         }

src/main/java/org/apache/commons/io/filefilter/NameFileFilter.java

@@ -94,9 +94,7 @@ public NameFileFilter(final List<String> names) {
      * @throws ClassCastException if the list does not contain Strings
      */
     public NameFileFilter(final List<String> names, final IOCase ioCase) {
-        if (names == null) {
-            throw new IllegalArgumentException("The list of names must not be null");
-        }
+        requireNonNull(names, "names");
         this.names = names.toArray(EMPTY_STRING_ARRAY);
         this.ioCase = toIOCase(ioCase);
     }

src/main/java/org/apache/commons/io/filefilter/NotFileFilter.java

@@ -42,9 +42,7 @@ public class NotFileFilter extends AbstractFileFilter implements Serializable {
      * @throws IllegalArgumentException if the filter is null
      */
     public NotFileFilter(final IOFileFilter filter) {
-        if (filter == null) {
-            throw new IllegalArgumentException("The filter must not be null");
-        }
+        requireNonNull(filter, "filter");
         this.filter = filter;
     }
 

src/main/java/org/apache/commons/io/filefilter/PrefixFileFilter.java

@@ -95,9 +95,7 @@ public PrefixFileFilter(final List<String> prefixes) {
      * @since 1.4
      */
     public PrefixFileFilter(final List<String> prefixes, final IOCase ioCase) {
-        if (prefixes == null) {
-            throw new IllegalArgumentException("The list of prefixes must not be null");
-        }
+        requireNonNull(prefixes, "prefixes");
         this.prefixes = prefixes.toArray(EMPTY_STRING_ARRAY);
         this.isCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }

src/main/java/org/apache/commons/io/filefilter/RegexFileFilter.java

@@ -78,9 +78,7 @@ public class RegexFileFilter extends AbstractFileFilter implements Serializable
      * @return a new Pattern.
      */
     private static Pattern compile(final String pattern, final int flags) {
-        if (pattern == null) {
-            throw new IllegalArgumentException("Pattern is missing");
-        }
+        requireNonNull(pattern, "pattern");
         return Pattern.compile(pattern, flags);
     }
 

src/main/java/org/apache/commons/io/filefilter/SuffixFileFilter.java

@@ -97,9 +97,7 @@ public SuffixFileFilter(final List<String> suffixes) {
      * @since 1.4
      */
     public SuffixFileFilter(final List<String> suffixes, final IOCase ioCase) {
-        if (suffixes == null) {
-            throw new IllegalArgumentException("The list of suffixes must not be null");
-        }
+        requireNonNull(suffixes, "suffixes");
         this.suffixes = suffixes.toArray(EMPTY_STRING_ARRAY);
         this.ioCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }

src/main/java/org/apache/commons/io/filefilter/WildcardFileFilter.java

@@ -104,9 +104,7 @@ public WildcardFileFilter(final List<String> wildcards) {
      * @throws ClassCastException if the list does not contain Strings
      */
     public WildcardFileFilter(final List<String> wildcards, final IOCase ioCase) {
-        if (wildcards == null) {
-            throw new IllegalArgumentException("The wildcard list must not be null");
-        }
+        requireNonNull(wildcards, "wildcards");
         this.wildcards = wildcards.toArray(EMPTY_STRING_ARRAY);
         this.ioCase = IOCase.value(ioCase, IOCase.SENSITIVE);
     }

src/main/java/org/apache/commons/io/filefilter/WildcardFilter.java

@@ -92,9 +92,7 @@ public class WildcardFilter extends AbstractFileFilter implements Serializable {
      * @throws ClassCastException if the list does not contain Strings
      */
     public WildcardFilter(final List<String> wildcards) {
-        if (wildcards == null) {
-            throw new IllegalArgumentException("The wildcard list must not be null");
-        }
+        requireNonNull(wildcards, "wildcards");
         this.wildcards = wildcards.toArray(EMPTY_STRING_ARRAY);
     }
 
@@ -105,9 +103,7 @@ public WildcardFilter(final List<String> wildcards) {
      * @throws IllegalArgumentException if the pattern is null
      */
     public WildcardFilter(final String wildcard) {
-        if (wildcard == null) {
-            throw new IllegalArgumentException("The wildcard must not be null");
-        }
+        requireNonNull(wildcard, "wildcard");
         this.wildcards = new String[] { wildcard };
     }
 
@@ -118,9 +114,7 @@ public WildcardFilter(final String wildcard) {
      * @throws IllegalArgumentException if the pattern array is null
      */
     public WildcardFilter(final String... wildcards) {
-        if (wildcards == null) {
-            throw new IllegalArgumentException("The wildcard array must not be null");
-        }
+        requireNonNull(wildcards, "wildcards");
         this.wildcards = wildcards.clone();
     }