JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2000, 2018, 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
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

package sun.jvm.hotspot.oops;

import java.io.*;
import java.util.*;
import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.types.*;
import sun.jvm.hotspot.utilities.*;

// A Symbol is a canonicalized string.
// All Symbols reside in global symbolTable.

public class Symbol extends VMObject {
  static {
    VM.registerVMInitializedObserver(new Observer() {
        public void update(Observable o, Object data) {
          initialize(VM.getVM().getTypeDataBase());
        }
      });
  }

  private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
    Type type  = db.lookupType("Symbol");
    lengthAndRefcount = type.getCIntegerField("_length_and_refcount");
    baseOffset = type.getField("_body").getOffset();
    idHash = type.getCIntegerField("_identity_hash");
  }

  public static Symbol create(Address addr) {
    if (addr == null) {
      return null;
    }
    return new Symbol(addr);
  }

  Symbol(Address addr) {
    super(addr);
  }

  public boolean isSymbol()            { return true; }

  private static long baseOffset; // tells where the array part starts

  // Fields
  private static CIntegerField lengthAndRefcount;

  // Accessors for declared fields
  public long getLength() {
    long i = lengthAndRefcount.getValue(this.addr);
    return (i >> 16) & 0xffff;
  }

  public byte getByteAt(long index) {
    return addr.getJByteAt(baseOffset + index);
  }
  // _identity_hash is a short
  private static CIntegerField idHash;

  public long identityHash() {
    long addr_value = getAddress().asLongValue();
    long addr_bits =
      (addr_value >> (VM.getVM().getLogMinObjAlignmentInBytes() + 3)) & 0xffffffffL;
    int  length = (int)getLength();
    int  byte0 = getByteAt(0);
    int  byte1 = getByteAt(1);
    long id_hash = 0xffffL & (long)idHash.getValue(this.addr);
    return (id_hash |
      ((addr_bits ^ (length << 8) ^ ((byte0 << 8) | byte1)) << 16)) & 0xffffffffL;
  }

  public boolean equals(byte[] modUTF8Chars) {
    int l = (int) getLength();
    if (l != modUTF8Chars.length) return false;
    while (l-- > 0) {
      if (modUTF8Chars[l] != getByteAt(l)) return false;
    }
    if (Assert.ASSERTS_ENABLED) {
      Assert.that(l == -1, "we should be at the beginning");
    }
    return true;
  }

  public boolean equals(String string) {
    return asString().equals(string);
  }

  public byte[] asByteArray() {
    int length = (int) getLength();
    byte [] result = new byte [length];
    for (int index = 0; index < length; index++) {
      result[index] = getByteAt(index);
    }
    return result;
  }

  public String asString() {
    // Decode the byte array and return the string.
    try {
      return readModifiedUTF8(asByteArray());
    } catch(Exception e) {
      System.err.println(addr);
      e.printStackTrace();
      return null;
    }
  }

  public boolean startsWith(String str) {
    return asString().startsWith(str);
  }

  public void printValueOn(PrintStream tty) {
    tty.print("#" + asString());
  }

  /** Note: this comparison is used for vtable sorting only; it
      doesn't matter what order it defines, as long as it is a total,
      time-invariant order Since Symbol* are in C_HEAP, their
      relative order in memory never changes, so use address
      comparison for speed. */
  public long fastCompare(Symbol other) {

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