jdk/src/java.base/share/classes/java/lang/classfile/ClassReader.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.lang.classfile;

import java.lang.classfile.constantpool.ClassEntry;
import java.lang.classfile.constantpool.ConstantPool;
import java.lang.classfile.constantpool.ConstantPoolException;
import java.lang.classfile.constantpool.PoolEntry;
import java.lang.classfile.constantpool.Utf8Entry;
import jdk.internal.classfile.impl.ClassReaderImpl;

import java.util.Optional;
import java.util.function.Function;
import jdk.internal.javac.PreviewFeature;

/**
 * Supports reading from a classfile.  Methods are provided to read data of
 * various numeric types (e.g., {@code u2}, {@code u4}) at a given offset within
 * the classfile, copying raw bytes, and reading constant pool entries.
 * Encapsulates additional reading context such as mappers for custom attributes
 * and processing options.
 *
 * @since 22
 */
@PreviewFeature(feature = PreviewFeature.Feature.CLASSFILE_API)
public sealed interface ClassReader extends ConstantPool
        permits ClassReaderImpl {

    // Processing context

    /**
     * {@return the table of custom attribute mappers}  This is derived from
     * the processing option {@link ClassFile.AttributeMapperOption}.
     */
    Function<Utf8Entry, AttributeMapper<?>> customAttributes();

    // Class context

    /** {@return the access flags for the class, as a bit mask } */
    int flags();

    /** {@return the constant pool entry describing the name of class} */
    ClassEntry thisClassEntry();

    /** {@return the constant pool entry describing the name of the superclass, if any} */
    Optional<ClassEntry> superclassEntry();

    /** {@return the length of the classfile, in bytes} */
    int classfileLength();

    // Constant pool

    /**
     * {@return the constant pool entry whose index is given at the specified
     * offset within the classfile}
     *
     * @apiNote
     * If only a particular type of entry is expected, use {@link #readEntry(
     * int, Class) readEntry(int, Class)}.
     *
     * @param offset the offset of the index within the classfile
     * @throws ConstantPoolException if the index is out of range of the
     *         constant pool size, or zero
     */
    PoolEntry readEntry(int offset);

    /**
     * {@return the constant pool entry of a given type whose index is given
     * at the specified offset within the classfile}
     * @param <T> the entry type
     * @param offset the offset of the index within the classfile
     * @param cls the entry type
     * @throws ConstantPoolException if the index is out of range of the
     *         constant pool size, or zero, or the entry is not of the given type
     */
    <T extends PoolEntry> T readEntry(int offset, Class<T> cls);

    /**
     * {@return the constant pool entry whose index is given at the specified
     * offset within the classfile, or null if the index at the specified
     * offset is zero}
     *
     * @apiNote
     * If only a particular type of entry is expected, use {@link #readEntryOrNull(
     * int, Class) readEntryOrNull(int, Class)}.
     *
     * @param offset the offset of the index within the classfile
     * @throws ConstantPoolException if the index is out of range of the
     *         constant pool size
     */
    PoolEntry readEntryOrNull(int offset);

    /**
     * {@return the constant pool entry of a given type whose index is given
     * at the specified offset within the classfile, or null if the index at
     * the specified offset is zero}
     *
     * @param <T> the entry type
     * @param offset the offset of the index within the classfile
     * @param cls the entry type
     * @throws ConstantPoolException if the index is out of range of the
     *         constant pool size, or zero, or the entry is not of the given type
     * @since 23
     */
    <T extends PoolEntry> T readEntryOrNull(int offset, Class<T> cls);

    /**
     * {@return the unsigned byte at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    int readU1(int offset);

    /**
     * {@return the unsigned short at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    int readU2(int offset);

    /**
     * {@return the signed byte at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    int readS1(int offset);

    /**
     * {@return the signed byte at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    int readS2(int offset);

    /**
     * {@return the signed int at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    int readInt(int offset);

    /**
     * {@return the signed long at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    long readLong(int offset);

    /**
     * {@return the float value at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    float readFloat(int offset);

    /**
     * {@return the double value at the specified offset within the classfile}
     * @param offset the offset within the classfile
     */
    double readDouble(int offset);

    /**
     * {@return a copy of the bytes at the specified range in the classfile}
     * @param offset the offset within the classfile
     * @param len the length of the range
     */
    byte[] readBytes(int offset, int len);

    /**
     * Copy a range of bytes from the classfile to a {@link BufWriter}
     *
     * @param buf the {@linkplain BufWriter}
     * @param offset the offset within the classfile
     * @param len the length of the range
     */
    void copyBytesTo(BufWriter buf, int offset, int len);
}