一、说明

二、主要的类与方法

解析和填充符号表这个过程主要由com.sun.tools.javac.comp.Entry及com.sun.tools.javac.comp.MemberEnter两个类来实现的。  

com.sun.tools.javac.comp.Entry 主要的方法如下：

/**
     * 访问类声明
     */
    public void visitClassDef(JCClassDecl tree) {
        Symbol owner = env.info.scope.owner;
        Scope enclScope = enterScope(env);
        ClassSymbol c;
        if (owner.kind == PCK) {
            // We are seeing a toplevel class.
            PackageSymbol packge = (PackageSymbol)owner;
            for (Symbol q = packge; q != null && q.kind == PCK; q = q.owner)
                q.flags_field |= EXISTS;
            c = reader.enterClass(tree.name, packge);
            packge.members().enterIfAbsent(c);
            if ((tree.mods.flags & PUBLIC) != 0 && !classNameMatchesFileName(c, env)) {
                log.error(tree.pos(),
                          "class.public.should.be.in.file", tree.name);
            }
        } else {
            if (tree.name.len != 0 &&
                !chk.checkUniqueClassName(tree.pos(), tree.name, enclScope)) {
                result = null;
                return;
            }
            if (owner.kind == TYP) {
                // We are seeing a member class.
                c = reader.enterClass(tree.name, (TypeSymbol)owner);
                if ((owner.flags_field & INTERFACE) != 0) {
                    tree.mods.flags |= PUBLIC | STATIC;
                }
            } else {
                // We are seeing a local class.
                c = reader.defineClass(tree.name, owner);
                c.flatname = chk.localClassName(c);
                if (c.name.len != 0)
                    chk.checkTransparentClass(tree.pos(), c, env.info.scope);
            }
        }
        tree.sym = c;

        // Enter class into `compiled' table and enclosing scope.
        if (chk.compiled.get(c.flatname) != null) {
            duplicateClass(tree.pos(), c);
            result = new ErrorType(tree.name, (TypeSymbol)owner);
            tree.sym = (ClassSymbol)result.tsym;
            return;
        }
        chk.compiled.put(c.flatname, c);
        enclScope.enter(c);

        // Set up an environment for class block and store in `typeEnvs'
        // table, to be retrieved later in memberEnter and attribution.
        Env<AttrContext> localEnv = classEnv(tree, env);
        typeEnvs.put(c, localEnv);

        // Fill out class fields.
        c.completer = memberEnter;
        c.flags_field = chk.checkFlags(tree.pos(), tree.mods.flags, c, tree);
        c.sourcefile = env.toplevel.sourcefile;
        c.members_field = new Scope(c);

        ClassType ct = (ClassType)c.type;
        if (owner.kind != PCK && (c.flags_field & STATIC) == 0) {
            // We are seeing a local or inner class.
            // Set outer_field of this class to closest enclosing class
            // which contains this class in a non-static context
            // (its "enclosing instance class"), provided such a class exists.
            Symbol owner1 = owner;
            while ((owner1.kind & (VAR | MTH)) != 0 &&
                   (owner1.flags_field & STATIC) == 0) {
                owner1 = owner1.owner;
            }
            if (owner1.kind == TYP) {
                ct.setEnclosingType(owner1.type);
            }
        }

        // Enter type parameters.
        ct.typarams_field = classEnter(tree.typarams, localEnv);

        // Add non-local class to uncompleted, to make sure it will be
        // completed later.
        if (!c.isLocal() && uncompleted != null) uncompleted.append(c);
//      System.err.println("entering " + c.fullname + " in " + c.owner);//DEBUG

        // Recursively enter all member classes.
        classEnter(tree.defs, localEnv);

        result = c.type;
    }
	
	 /** Main method: enter all classes in a list of toplevel trees.
     *  @param trees      The list of trees to be processed.
     */
    public void main(List<JCCompilationUnit> trees) {
        complete(trees, null);
    }

    /**
     * Main method: enter one class from a list of toplevel trees and
     *  place the rest on uncompleted for later processing.
     *  @param trees      The list of trees to be processed.
     *  @param c          The class symbol to be processed.
     */
    public void complete(List<JCCompilationUnit> trees, ClassSymbol c) {
        annotate.enterStart();
        ListBuffer<ClassSymbol> prevUncompleted = uncompleted;
        if (memberEnter.completionEnabled) uncompleted = new ListBuffer<ClassSymbol>();

        try {
            // enter all classes, and construct uncompleted list
            classEnter(trees, null);

            // complete all uncompleted classes in memberEnter
            if  (memberEnter.completionEnabled) {
                while (uncompleted.nonEmpty()) {
                    ClassSymbol clazz = uncompleted.next();
                    if (c == null || c == clazz || prevUncompleted == null)
                        clazz.complete();
                    else
                        //将类符号放入prevUncompleted列表(uncompleted列表)
                        prevUncompleted.append(clazz);
                }

                // if there remain any unimported toplevels (these must have
                // no classes at all), process their import statements as well.
                /**
                 * uncompleted列表没有的符号(除类符号外)，根据improt声明，给顶级抽象树都添加了一个MemberEnter对象
                 * 这些符号(包括类的参数类型符号也就是泛型、父类符号、接口类型符等)
                 */
                for (JCCompilationUnit tree : trees) {
                    if (tree.starImportScope.elems == null) {
                        JavaFileObject prev = log.useSource(tree.sourcefile);
                        Env<AttrContext> env = typeEnvs.get(tree);
                        if (env == null)
                            env = topLevelEnv(tree);
                        memberEnter.memberEnter(tree, env);
                        log.useSource(prev);
                    }
                }
            }
        } finally {
        	//prevUncompleted列表赋值给uncompleted列表
            uncompleted = prevUncompleted;
            annotate.enterDone();
        }
    }
 

com.sun.tools.javac.comp.MemberEnter 主要的方法如下:

/** Complete entering a class.
     *  将未处理列表中的所有符号都解析到各自的类符号表中
     *  @param sym         The symbol of the class to be completed.
     */
    public void complete(Symbol sym) throws CompletionFailure {
        // Suppress some (recursive) MemberEnter invocations
        if (!completionEnabled) {
            // Re-install same completer for next time around and return.
            assert (sym.flags() & Flags.COMPOUND) == 0;
            sym.completer = this;
            return;
        }

        ClassSymbol c = (ClassSymbol)sym;
        ClassType ct = (ClassType)c.type;
        Env<AttrContext> env = enter.typeEnvs.get(c);
        JCClassDecl tree = (JCClassDecl)env.tree;
        boolean wasFirst = isFirst;
        isFirst = false;

        JavaFileObject prev = log.useSource(env.toplevel.sourcefile);
        try {
            // Save class environment for later member enter (2) processing.
            halfcompleted.append(env);

            // If this is a toplevel-class, make sure any preceding import
            // clauses have been seen.
            if (c.owner.kind == PCK) {
                memberEnter(env.toplevel, env.enclosing(JCTree.TOPLEVEL));
                todo.append(env);
            }

            // Mark class as not yet attributed.
            c.flags_field |= UNATTRIBUTED;

            if (c.owner.kind == TYP)
                c.owner.complete();

            // create an environment for evaluating the base clauses
            Env<AttrContext> baseEnv = baseEnv(tree, env);

            // Determine supertype.
            Type supertype =
                (tree.extending != null)
                ? attr.attribBase(tree.extending, baseEnv, true, false, true)
                : ((tree.mods.flags & Flags.ENUM) != 0 && !target.compilerBootstrap(c))
                ? attr.attribBase(enumBase(tree.pos, c), baseEnv,
                                  true, false, false)
                : (c.fullname == names.java_lang_Object)
                ? Type.noType
                : syms.objectType;
            ct.supertype_field = supertype;

            // Determine interfaces.
            ListBuffer<Type> interfaces = new ListBuffer<Type>();
            Set<Type> interfaceSet = new HashSet<Type>();
            List<JCExpression> interfaceTrees = tree.implementing;
            if ((tree.mods.flags & Flags.ENUM) != 0 && target.compilerBootstrap(c)) {
                // add interface Comparable<T>
                interfaceTrees =
                    interfaceTrees.prepend(make.Type(new ClassType(syms.comparableType.getEnclosingType(),
                                                                   List.of(c.type),
                                                                   syms.comparableType.tsym)));
                // add interface Serializable
                interfaceTrees =
                    interfaceTrees.prepend(make.Type(syms.serializableType));
            }
            for (JCExpression iface : interfaceTrees) {
                Type i = attr.attribBase(iface, baseEnv, false, true, true);
                if (i.tag == CLASS) {
                    interfaces.append(i);
                    chk.checkNotRepeated(iface.pos(), types.erasure(i), interfaceSet);
                }
            }
            if ((c.flags_field & ANNOTATION) != 0)
                ct.interfaces_field = List.of(syms.annotationType);
            else
                ct.interfaces_field = interfaces.toList();

            if (c.fullname == names.java_lang_Object) {
                if (tree.extending != null) {
                    chk.checkNonCyclic(tree.extending.pos(),
                                       supertype);
                    ct.supertype_field = Type.noType;
                }
                else if (tree.implementing.nonEmpty()) {
                    chk.checkNonCyclic(tree.implementing.head.pos(),
                                       ct.interfaces_field.head);
                    ct.interfaces_field = List.nil();
                }
            }

            // Annotations.
            // In general, we cannot fully process annotations yet,  but we
            // can attribute the annotation types and then check to see if the
            // @Deprecated annotation is present.
            attr.attribAnnotationTypes(tree.mods.annotations, baseEnv);
            if (hasDeprecatedAnnotation(tree.mods.annotations))
                c.flags_field |= DEPRECATED;
            annotateLater(tree.mods.annotations, baseEnv, c);

            attr.attribTypeVariables(tree.typarams, baseEnv);

            chk.checkNonCyclic(tree.pos(), c.type);

            /**
             * 增加一个默认的构造方法(当类没有构造方法时)
             */
            if ((c.flags() & INTERFACE) == 0 &&
                !TreeInfo.hasConstructors(tree.defs)) {
                List<Type> argtypes = List.nil();
                List<Type> typarams = List.nil();
                List<Type> thrown = List.nil();
                long ctorFlags = 0;
                boolean based = false;
                if (c.name.len == 0) {
                    JCNewClass nc = (JCNewClass)env.next.tree;
                    if (nc.constructor != null) {
                        Type superConstrType = types.memberType(c.type,
                                                                nc.constructor);
                        argtypes = superConstrType.getParameterTypes();
                        typarams = superConstrType.getTypeArguments();
                        ctorFlags = nc.constructor.flags() & VARARGS;
                        if (nc.encl != null) {
                            argtypes = argtypes.prepend(nc.encl.type);
                            based = true;
                        }
                        thrown = superConstrType.getThrownTypes();
                    }
                }
                JCTree constrDef = DefaultConstructor(make.at(tree.pos), c,
                                                    typarams, argtypes, thrown,
                                                    ctorFlags, based);
                tree.defs = tree.defs.prepend(constrDef);
            }

            // If this is a class, enter symbols for this and super into
            // current scope.
            if ((c.flags_field & INTERFACE) == 0) {
                VarSymbol thisSym =
                    new VarSymbol(FINAL | HASINIT, names._this, c.type, c);
                thisSym.pos = Position.FIRSTPOS;
                env.info.scope.enter(thisSym);
                if (ct.supertype_field.tag == CLASS) {
                    VarSymbol superSym =
                        new VarSymbol(FINAL | HASINIT, names._super,
                                      ct.supertype_field, c);
                    superSym.pos = Position.FIRSTPOS;
                    env.info.scope.enter(superSym);
                }
            }

            // check that no package exists with same fully qualified name,
            // but admit classes in the unnamed package which have the same
            // name as a top-level package.
            if (checkClash &&
                c.owner.kind == PCK && c.owner != syms.unnamedPackage &&
                reader.packageExists(c.fullname))
                {
                    log.error(tree.pos, "clash.with.pkg.of.same.name", c);
                }

        } catch (CompletionFailure ex) {
            chk.completionError(tree.pos(), ex);
        } finally {
            log.useSource(prev);
        }

        // Enter all member fields and methods of a set of half completed
        // classes in a second phase.
        if (wasFirst) {
            try {
                while (halfcompleted.nonEmpty()) {
                    finish(halfcompleted.next());
                }
            } finally {
                isFirst = true;
            }

            // commit pending annotations
            annotate.flush();
        }
    }

三、过程及简单源码解析

第一个阶段:

整个操作的方法调用过程如下：

上面这个过程是访问者模式的一种实现。
Enter是一个JCTree.Visitor.Enter.classEnter(l.head, env)调用JCTree.accept(Visitor v)，而accept方法又是调用的Visitor类里面的visitXXX()方法，而这些方法的实现又是在Enter类中。也就是Enter.visitClassDef(JCClassDecl tree)方法，在这个方法中，会将类符号放入uncompleted列表; 


visitClassDef(JCClassDecl tree)方法主要做三件事：

1、将类符号(当前类)填入类自身的符号表，添加了一个MemberEnter对象
       

        // Enter class into `compiled' table and enclosing scope.
        if (chk.compiled.get(c.flatname) != null) {
            duplicateClass(tree.pos(), c);
            result = new ErrorType(tree.name, (TypeSymbol)owner);
            tree.sym = (ClassSymbol)result.tsym;
            return;
        }
        chk.compiled.put(c.flatname, c);
        enclScope.enter(c);
		
		// Set up an environment for class block and store in `typeEnvs'
        // table, to be retrieved later in memberEnter and attribution.
        Env<AttrContext> localEnv = classEnv(tree, env);
        typeEnvs.put(c, localEnv);


        // Fill out class fields.
        c.completer = memberEnter;
        c.flags_field = chk.checkFlags(tree.pos(), tree.mods.flags, c, tree);
        c.sourcefile = env.toplevel.sourcefile;
        c.members_field = new Scope(c);

        // Enter type parameters.
        ct.typarams_field = classEnter(tree.typarams, localEnv);

if (!c.isLocal() && uncompleted != null) uncompleted.append(c);

memberEnter.memberEnter(tree, env);	

第二个阶段:

整个操作的方法调用过程如下：



Enter是一个JCTree.Visitor.Enter.classEnter(l.head, env)调用JCTree.accept(Visitor v)，而accept方法又是调用的Visitor类里面的visitXXX()方法，而这些方法的实现又是在Enter类中。也就是Enter.visitClassDef(JCClassDecl tree)方法，在这个方法中，会将类符号解析和填入类自身的符号表。




最后，enter把所有的顶层类（top-level classes）放到一个todo-queue中。