Polish JarFile to extra anonymous inner class

See gh-20882

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarFile.java

@@ -192,19 +192,7 @@ public class JarFile extends java.util.jar.JarFile {
 	@Override
 	public Enumeration<java.util.jar.JarEntry> entries() {
 		final Iterator<JarEntry> iterator = this.entries.iterator();
-		return new Enumeration<java.util.jar.JarEntry>() {
-
-			@Override
-			public boolean hasMoreElements() {
-				return iterator.hasNext();
-			}
-
-			@Override
-			public java.util.jar.JarEntry nextElement() {
-				return iterator.next();
-			}
-
-		};
+		return new EnumerationJarEntry(iterator);
 	}
 
 	public JarEntry getJarEntry(CharSequence name) {
@@ -421,4 +409,33 @@ public class JarFile extends java.util.jar.JarFile {
 
 	}
 
+	/**
+	 * The type Enumeration jar entry.
+	 */
+	static class EnumerationJarEntry implements Enumeration<java.util.jar.JarEntry> {
+
+		/**
+		 * The Iterator.
+		 */
+		Iterator<JarEntry> iterator;
+
+		/**
+		 * Instantiates a new Enumeration jar entry.
+		 *
+		 * @param iterator the iterator
+		 */
+		EnumerationJarEntry(Iterator<JarEntry> iterator) {
+			this.iterator = iterator;
+		}
+
+		@Override
+		public boolean hasMoreElements() {
+			return this.iterator.hasNext();
+		}
+
+		@Override
+		public java.util.jar.JarEntry nextElement() {
+			return this.iterator.next();
+		}
+	}
 }