8311175: Move BufWriter::asByteBuffer to BufWriterImpl

Reviewed-by: asotona

src/java.base/share/classes/java/lang/classfile/BufWriter.java

@@ -24,7 +24,6 @@
  */
 package java.lang.classfile;
 
-import java.nio.ByteBuffer;
 import java.util.List;
 
 import java.lang.classfile.constantpool.ConstantPool;
@@ -192,11 +191,6 @@ public sealed interface BufWriter
      */
     int size();
 
-    /**
-     * {@return a {@link java.nio.ByteBuffer ByteBuffer} view of the bytes in the buffer}
-     */
-    ByteBuffer asByteBuffer();
-
     /**
      * Copy the contents of the buffer into a byte array.
      *

src/java.base/share/classes/jdk/internal/classfile/impl/BufWriterImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -171,9 +171,8 @@ public final class BufWriterImpl implements BufWriter {
         return offset;
     }
 
-    @Override
     public ByteBuffer asByteBuffer() {
-        return ByteBuffer.wrap(elems, 0, offset);
+        return ByteBuffer.wrap(elems, 0, offset).slice();
     }
 
     @Override

src/java.base/share/classes/jdk/internal/classfile/impl/StackCounter.java

@@ -51,7 +51,7 @@ public final class StackCounter {
                 dcb.methodInfo.methodName().stringValue(),
                 dcb.methodInfo.methodTypeSymbol(),
                 (dcb.methodInfo.methodFlags() & ACC_STATIC) != 0,
-                dcb.bytecodesBufWriter.asByteBuffer().slice(0, dcb.bytecodesBufWriter.size()),
+                ((BufWriterImpl) dcb.bytecodesBufWriter).asByteBuffer(),
                 dcb.constantPool,
                 dcb.handlers);
     }

src/java.base/share/classes/jdk/internal/classfile/impl/StackMapGenerator.java

@@ -151,7 +151,7 @@ public final class StackMapGenerator {
                 dcb.methodInfo.methodName().stringValue(),
                 dcb.methodInfo.methodTypeSymbol(),
                 (dcb.methodInfo.methodFlags() & ACC_STATIC) != 0,
-                dcb.bytecodesBufWriter.asByteBuffer().slice(0, dcb.bytecodesBufWriter.size()),
+                ((BufWriterImpl) dcb.bytecodesBufWriter).asByteBuffer(),
                 dcb.constantPool,
                 dcb.context,
                 dcb.handlers);