Scope及其子類介紹
阿新 • • 發佈：2018-06-23
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之前寫的文章：
關於作用域範圍Scope
Scope及相關的子類如下：
同時有些Scope還繼承了Scope.ScopeListener類，如下：
1、StarImportScope及ImportScope
在JCCompilationUnit中定義了兩個屬性，其類型就是這兩個類型：
public ImportScope namedImportScope;
public StarImportScope starImportScope;
但在初始化JCCompilationUnit語法節點時並不初始化這兩個屬性，而是在Enter的如下類中進行初始化，代碼如下：
/** Create a fresh environment for toplevels. * @param tree The toplevel tree. */ public Env<AttrContext> topLevelEnv(JCCompilationUnit tree) { tree.namedImportScope = new ImportScope(tree.packge); tree.starImportScope = new StarImportScope(tree.packge); Env<AttrContext> localEnv = new Env<AttrContext>(tree, new AttrContext()); localEnv.toplevel = tree; localEnv.enclClass = predefClassDef; // JCCompilationUnit的環境Scope中使用的是namedImportScope localEnv.info.scope = tree.namedImportScope; localEnv.info.lint = lint; return localEnv; }
Scope最重要的作用就是用來查找特定範圍內定義的符號，而這些符號的填充在MemberEnter類中完成的。首先看StarImportScope的填充，代碼如下：
/** Import all classes of a class or package on demand. * @param pos Position to be used for error reporting. * @param tsym The class or package the members of which are imported. * @param toScope The (import) scope in which imported classes are entered. */ private void importAll(int pos, final TypeSymbol tsym, Env<AttrContext> env) { // Check that packages imported from exist (JLS ???). // 在調用tsym.members()會調用complete()方法來完成這個符號屬性的填充 if (tsym.kind == PCK01 && tsym.members().elems == null && !tsym.exists()) { // If we can‘t find java.lang, exit immediately. if (((PackageSymbol)tsym).fullname.equals(names.java_lang)) { // 致命錯誤: 在類路徑或引導類路徑中找不到程序包 java.lang JCDiagnostic msg = diags.fragment("fatal.err.no.java.lang"); throw new FatalError(msg); } else { // 程序包{0}不存在 log.error(JCDiagnosticFlag.RESOLVE_ERROR, pos, "doesnt.exist", tsym); } } Scope sp = tsym.members(); env.toplevel.starImportScope.importAll(sp); }
每個JCCompilationUnit編譯單元通過import導入需要的依賴，有一個是默認導入的，就是java.lang.*下面的定義的類，而代碼sp中包含的類符號如下：
Scope[ Void,VirtualMachineError, VerifyError,UnsupportedOperationException, UnsupportedClassVersionError,UnsatisfiedLinkError, UnknownError, TypeNotPresentException, Throwable, Throwable$WrappedPrintWriter, Throwable$WrappedPrintStream,Throwable$SentinelHolder, Throwable$PrintStreamOrWriter,ThreadLocal, ThreadLocal$ThreadLocalMap,ThreadLocal$ThreadLocalMap$Entry, ThreadGroup,ThreadDeath, Thread, Thread$WeakClassKey, Thread$UncaughtExceptionHandler, Thread$State, Thread$Caches, Terminator, SystemClassLoaderAction, System, SuppressWarnings, StringIndexOutOfBoundsException, StringCoding, StringCoding$StringEncoder, StringCoding$StringDecoder, StringBuilder, StringBuffer, String, String$CaseInsensitiveComparator, StrictMath, StackTraceElement, StackOverflowError, Shutdown,Shutdown$Lock, Short, Short$ShortCache, SecurityManager, SecurityException, SafeVarargs, RuntimePermission, RuntimeException, Runtime, Runnable, ReflectiveOperationException, Readable, ProcessImpl, ProcessImpl$LazyPattern, ProcessEnvironment, ProcessEnvironment$NameComparator, ProcessEnvironment$EntryComparator, ProcessEnvironment$CheckedValues, ProcessEnvironment$CheckedKeySet, ProcessEnvironment$CheckedEntrySet, ProcessEnvironment$CheckedEntry, ProcessBuilder, ProcessBuilder$Redirect, ProcessBuilder$Redirect$Type,ProcessBuilder$NullOutputStream, ProcessBuilder$NullInputStream, Process, Package, Override, OutOfMemoryError, Object,NumberFormatException, Number, NullPointerException, NoSuchMethodException, NoSuchMethodError, NoSuchFieldException, NoSuchFieldError, NoClassDefFoundError, NegativeArraySizeException, Math, Long, Long$LongCache, LinkageError, Iterable, InterruptedException, InternalError, Integer, Integer$IntegerCache, InstantiationException, InstantiationError, InheritableThreadLocal, IndexOutOfBoundsException, IncompatibleClassChangeError,IllegalThreadStateException, IllegalStateException, IllegalMonitorStateException, IllegalArgumentException, IllegalAccessException, IllegalAccessError, Float, ExceptionInInitializerError, Exception, Error, EnumConstantNotPresentException, Enum, Double, Deprecated, ConditionalSpecialCasing, ConditionalSpecialCasing$Entry, Compiler, Comparable, Cloneable,CloneNotSupportedException, ClassValue, ClassValue$Version, ClassValue$Identity, ClassValue$Entry, ClassValue$ClassValueMap,ClassNotFoundException, ClassLoaderHelper, ClassLoader, ClassLoader$ParallelLoaders, ClassLoader$NativeLibrary, ClassFormatError, ClassCircularityError, ClassCastException,Class, Class$SecurityManagerHelper, Class$ReflectionData, Class$MethodArray, Class$EnclosingMethodInfo, Class$Atomic, CharacterName, CharacterDataUndefined, CharacterDataPrivateUse, CharacterDataLatin1, CharacterData0E, CharacterData02,CharacterData01, CharacterData00, CharacterData, Character, Character$UnicodeScript, Character$UnicodeBlock, Character$Subset, Character$CharacterCache, CharSequence, Byte, Byte$ByteCache, BootstrapMethodError, Boolean, AutoCloseable, AssertionStatusDirectives, AssertionError, ArrayStoreException, ArrayIndexOutOfBoundsException, ArithmeticException, ApplicationShutdownHooks, Appendable, AbstractStringBuilder, AbstractMethodError ]
調用了StarImportScope的importAll()方法，傳入了sp參數：importAll()方法代碼如下：
public class StarImportScope extends ImportScope implements Scope.ScopeListener {
public StarImportScope(Symbol owner) {
super(owner);
}
public void importAll (Scope fromScope) {
for (Scope.Entry e = fromScope.elems; e != null; e = e.sibling) {
if (e.sym.kind == Kinds.TYP02 && !includes(e.sym)) {
enter(e.sym, fromScope);
}
}
// Register to be notified when imported items are removed
fromScope.addScopeListener(this);
}
public void symbolRemoved(Symbol sym, Scope s) {
remove(sym);
}
public void symbolAdded(Symbol sym, Scope s) { }
}
將sp中的所有符號導入StarImportScope中，並且StarImportScope中的table屬性（Entry[]類型）中的元素為ImportEntry，如下部分截圖：
說一下靜態導入和非靜態導入：
import java.io.*;
import java.math.BigDecimal;
import static com.test19.TestStatic.*;
import static com.test19.TestStatic.method; // 導入
public class TestScope{
public void t(){
InputStream p;
BigDecimal d;
int b = v;
method();
}
}
無論靜態還是非靜態導入，最終都會調用MemberEnter類中的visitImport()方法，
Scope及其子類介紹