diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/standard/SpelCompiler.java b/spring-expression/src/main/java/org/springframework/expression/spel/standard/SpelCompiler.java
index a83bf5dbe0..847da65a73 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/standard/SpelCompiler.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/standard/SpelCompiler.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -63,18 +63,20 @@ import org.springframework.util.StringUtils;
  * <p>Individual expressions can be compiled by calling {@code SpelCompiler.compile(expression)}.
  *
  * @author Andy Clement
+ * @author Juergen Hoeller
  * @since 4.1
  */
 public final class SpelCompiler implements Opcodes {
 
-	private static final Log logger = LogFactory.getLog(SpelCompiler.class);
-
 	private static final int CLASSES_DEFINED_LIMIT = 100;
 
+	private static final Log logger = LogFactory.getLog(SpelCompiler.class);
+
 	// A compiler is created for each classloader, it manages a child class loader of that
 	// classloader and the child is used to load the compiled expressions.
 	private static final Map<ClassLoader, SpelCompiler> compilers = new ConcurrentReferenceHashMap<>();
 
+
 	// The child ClassLoader used to load the compiled expression classes
 	private ChildClassLoader ccl;
 
@@ -90,7 +92,7 @@ public final class SpelCompiler implements Opcodes {
 	/**
 	 * Attempt compilation of the supplied expression. A check is made to see
 	 * if it is compilable before compilation proceeds. The check involves
-	 * visiting all the nodes in the expression Ast and ensuring enough state
+	 * visiting all the nodes in the expression AST and ensuring enough state
 	 * is known about them that bytecode can be generated for them.
 	 * @param expression the expression to compile
 	 * @return an instance of the class implementing the compiled expression,
@@ -125,7 +127,7 @@ public final class SpelCompiler implements Opcodes {
 
 	/**
 	 * Generate the class that encapsulates the compiled expression and define it.
-	 * The  generated class will be a subtype of CompiledExpression.
+	 * The generated class will be a subtype of CompiledExpression.
 	 * @param expressionToCompile the expression to be compiled
 	 * @return the expression call, or {@code null} if the decision was to opt out of
 	 * compilation during code generation
@@ -150,7 +152,7 @@ public final class SpelCompiler implements Opcodes {
 		// Create getValue() method
 		mv = cw.visitMethod(ACC_PUBLIC, "getValue",
 				"(Ljava/lang/Object;Lorg/springframework/expression/EvaluationContext;)Ljava/lang/Object;", null,
-				new String[ ]{"org/springframework/expression/EvaluationException"});
+				new String[] {"org/springframework/expression/EvaluationException"});
 		mv.visitCode();
 
 		CodeFlow cf = new CodeFlow(className, cw);
@@ -187,7 +189,7 @@ public final class SpelCompiler implements Opcodes {
 
 	/**
 	 * Load a compiled expression class. Makes sure the classloaders aren't used too much
-	 * because they anchor compiled classes in memory and prevent GC.  If you have expressions
+	 * because they anchor compiled classes in memory and prevent GC. If you have expressions
 	 * continually recompiling over time then by replacing the classloader periodically
 	 * at least some of the older variants can be garbage collected.
 	 * @param name the name of the class
@@ -202,6 +204,7 @@ public final class SpelCompiler implements Opcodes {
 		return (Class<? extends CompiledExpression>) this.ccl.defineClass(name, bytes);
 	}
 
+
 	/**
 	 * Factory method for compiler instances. The returned SpelCompiler will
 	 * attach a class loader as the child of the given class loader and this
@@ -222,10 +225,12 @@ public final class SpelCompiler implements Opcodes {
 	}
 
 	/**
-	 * Request that an attempt is made to compile the specified expression. It may fail if
-	 * components of the expression are not suitable for compilation or the data types
-	 * involved are not suitable for compilation. Used for testing.
-	 * @return true if the expression was successfully compiled
+	 * Request that an attempt is made to compile the specified expression.
+	 * It may fail if components of the expression are not suitable for compilation
+	 * or the data types involved are not suitable for compilation. Used for testing.
+	 * @param expression the expression to compile
+	 * @return {@code true} if the expression was successfully compiled,
+	 * {@code false} otherwise
 	 */
 	public static boolean compile(Expression expression) {
 		return (expression instanceof SpelExpression && ((SpelExpression) expression).compileExpression());
@@ -256,18 +261,21 @@ public final class SpelCompiler implements Opcodes {
 			super(NO_URLS, classLoader);
 		}
 
-		int getClassesDefinedCount() {
-			return this.classesDefinedCount;
-		}
-
 		public Class<?> defineClass(String name, byte[] bytes) {
 			Class<?> clazz = super.defineClass(name, bytes, 0, bytes.length);
 			this.classesDefinedCount++;
 			return clazz;
 		}
+
+		public int getClassesDefinedCount() {
+			return this.classesDefinedCount;
+		}
 	}
 
 
+	/**
+	 * An ASM ClassWriter extension bound to the SpelCompiler's ClassLoader.
+	 */
 	private class ExpressionClassWriter extends ClassWriter {
 
 		public ExpressionClassWriter() {