Java example source code file (LocalVariableTable.java)

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Java - Java tags/keywords

constantpool, dataoutputstream, ioexception, localvariable, localvariabletable

The LocalVariableTable.java Java example source code

/*
 * Copyright (c) 1995, 2003, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.tools.asm;

import sun.tools.java.*;
import java.io.IOException;
import java.io.DataOutputStream;

/**
 * This class is used to assemble the local variable table.
 *
 * WARNING: The contents of this source file are not part of any
 * supported API.  Code that depends on them does so at its own risk:
 * they are subject to change or removal without notice.
 *
 * @author Arthur van Hoff
 */
final
class LocalVariableTable {
    LocalVariable locals[] = new LocalVariable[8];
    int len;

    /**
     * Define a new local variable. Merge entries where possible.
     */
    void define(MemberDefinition field, int slot, int from, int to) {
        if (from >= to) {
            return;
        }
        for (int i = 0 ; i < len ; i++) {
            if ((locals[i].field == field) && (locals[i].slot == slot) &&
                (from <= locals[i].to) && (to >= locals[i].from)) {
                locals[i].from = Math.min(locals[i].from, from);
                locals[i].to = Math.max(locals[i].to, to);
                return;
            }
        }
        if (len == locals.length) {
            LocalVariable newlocals[] = new LocalVariable[len * 2];
            System.arraycopy(locals, 0, newlocals, 0, len);
            locals = newlocals;
        }
        locals[len++] = new LocalVariable(field, slot, from, to);
    }

    /**
     * Trim overlapping local ranges.  Java forbids shadowing of
     * locals in nested scopes, but non-nested scopes may still declare
     * locals with the same name.  Because local variable ranges are
     * computed using flow analysis as part of assembly, it isn't
     * possible to simply make sure variable ranges end where the
     * enclosing lexical scope ends.  This method makes sure that
     * variables with the same name don't overlap, giving priority to
     * fields with higher slot numbers that should have appeared later
     * in the source.
     */
    private void trim_ranges() {
        for (int i=0; i<len; i++) {
            for (int j=i+1; j<len; j++) {
                if ((locals[i].field.getName()==locals[j].field.getName())
                        && (locals[i].from <= locals[j].to)
                        && (locals[i].to >= locals[j].from)) {
                    // At this point we know that both ranges are
                    // the same name and there is also overlap or they abut
                    if (locals[i].slot < locals[j].slot) {
                        if (locals[i].from < locals[j].from) {
                          locals[i].to = Math.min(locals[i].to, locals[j].from);
                        } else {
                          // We've detected two local variables with the
                          // same name, and the one with the greater slot
                          // number starts before the other.  This order
                          // reversal may happen with locals with the same
                          // name declared in both a try body and an
                          // associated catch clause.  This is rare, and
                          // we give up.
                        }
                    } else if (locals[i].slot > locals[j].slot) {
                        if (locals[i].from > locals[j].from) {
                          locals[j].to = Math.min(locals[j].to, locals[i].from);
                        } else {
                          // Same situation as above; just give up.
                        }
                    } else {
                        // This case can happen if there are two variables
                        // with the same name and slot numbers, and ranges
                        // that abut.  AFAIK the only way this can occur
                        // is with multiple static initializers.  Punt.
                    }
                }
            }
        }
    }

    /**
     * Write out the data.
     */
    void write(Environment env, DataOutputStream out, ConstantPool tab) throws IOException {
        trim_ranges();
        out.writeShort(len);
        for (int i = 0 ; i < len ; i++) {
            //System.out.println("pc=" + locals[i].from + ", len=" + (locals[i].to - locals[i].from) + ", nm=" + locals[i].field.getName() + ", slot=" + locals[i].slot);
            out.writeShort(locals[i].from);
            out.writeShort(locals[i].to - locals[i].from);
            out.writeShort(tab.index(locals[i].field.getName().toString()));
            out.writeShort(tab.index(locals[i].field.getType().getTypeSignature()));
            out.writeShort(locals[i].slot);
        }
    }
}