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Scanner.java
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Scanner.java
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/*
* Copyright (c) 1999, 2011, 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 com.sun.tools.javac.parser;
import com.sun.tools.javac.code.Source;
import com.sun.tools.javac.file.JavacFileManager;
import com.sun.tools.javac.util.*;
import java.nio.CharBuffer;
import static com.sun.tools.javac.parser.Token.*;
import static com.sun.tools.javac.util.LayoutCharacters.*;
/**
* The lexical analyzer maps an input stream consisting of
* ASCII characters and Unicode escapes into a token sequence.
*
* <p><b>This is NOT part of any supported API.
* If you write code that depends on this, you do so at your own risk.
* This code and its internal interfaces are subject to change or
* deletion without notice.</b>
*/
public class Scanner implements Lexer {
/**
* Are surrogates supported?
*/
final static boolean surrogatesSupported = surrogatesSupported();
/* Output variables; set by nextToken():
*/
private static final boolean hexFloatsWork = hexFloatsWork();
private static boolean scannerDebug = false;
/**
* The log to be used for error reporting.
*/
private final Log log;
/**
* The name table.
*/
private final Names names;
/**
* The keyword table.
*/
private final Keywords keywords;
/**
* Has a @deprecated been encountered in last doc comment?
* this needs to be reset by client.
*/
protected boolean deprecatedFlag = false;
/**
* The token, set by nextToken().
*/
// 调用nextToken()方法生成的Token对象会赋值给一个名称为token的成员变量
private Token token;
/**
* Allow hex floating-point literals.
*/
private boolean allowHexFloats;
/**
* Allow binary literals.
*/
private boolean allowBinaryLiterals;
/**
* Allow underscores in literals.
*/
private boolean allowUnderscoresInLiterals;
/**
* The source language setting.
*/
private Source source;
/**
* The token's position, 0-based offset from beginning of text.
*/
private int pos;
/**
* Character position just after the last character of the token.
*/
private int endPos;
/**
* The last character position of the previous token.
*/
private int prevEndPos;
/**
* The position where a lexical error occurred;
*/
private int errPos = Position.NOPOS;
/**
* The name of an identifier or token:
*/
private Name name;
/**
* the radix of a numeric literal token.
*/
private int radix;
/**
* A character buffer for literals.
*/
// sbuf数组按顺序暂存读入的字符
private char[] sbuf = new char[128];
// sp指示了sbuf中下一个可用的位置
// 每次调用nextToken()方法，sp就会被初始化为0
private int sp;
/**
* The input buffer, index of next chacter to be read,
* index of one past last character in buffer.
*/
// 保存了从Java源文件中读入的所有字符,最后一个数组元素的值为EOI，EOI其实就是一个值为0x1A的常量，表示已经没有可读取的字符
private char[] buf;
// bp保存了buf数组中当前要处理的字符的位置，初始化时将bp设置为-1
private int bp;
// buflen保存了buf数组中可读字符的数量，或者说指向了buf数组中可读取字符的最大下标，不包括下标值为buflen的元素
private int buflen;
private int eofPos;
/**
* The current character.
*/
private char ch;
/**
* The buffer index of the last converted unicode character
*/
private int unicodeConversionBp = -1;
/**
* Common code for constructors.
*/
private Scanner(ScannerFactory fac) {
log = fac.log;
names = fac.names;
keywords = fac.keywords;
source = fac.source;
allowBinaryLiterals = source.allowBinaryLiterals();
allowHexFloats = source.allowHexFloats();
allowUnderscoresInLiterals = source.allowUnderscoresInLiterals();
}
/**
* Create a scanner from the input buffer. buffer must implement
* array() and compact(), and remaining() must be less than limit().
*/
protected Scanner(ScannerFactory fac, CharBuffer buffer) {
// JavacFileManager.toArray(buffer)：将buffer转化为数组
this(fac, JavacFileManager.toArray(buffer), buffer.limit());
}
/**
* Create a scanner from the input array. This method might
* modify the array. To avoid copying the input array, ensure
* that {@code inputLength < input.length} or
* {@code input[input.length -1]} is a white space character.
*
* @param fac the factory which created this Scanner
* @param input the input, might be modified
* @param inputLength the size of the input.
* Must be positive and less than or equal to input.length.
*/
protected Scanner(ScannerFactory fac, char[] input, int inputLength) {
this(fac);
eofPos = inputLength;
if (inputLength == input.length) {
if (input.length > 0 && Character.isWhitespace(input[input.length - 1])) {
inputLength--;
} else {
char[] newInput = new char[inputLength + 1];
System.arraycopy(input, 0, newInput, 0, input.length);
input = newInput;
}
}
buf = input;
buflen = inputLength;
buf[buflen] = EOI;
bp = -1;
// 在处理开始时，通常会调用scanChar()方法将bp值更新为下一个要处理字符的下标位置
// bp加1，要处理的ch致为buf的第一个字符
scanChar();
}
private static boolean hexFloatsWork() {
try {
Float.valueOf("0x1.0p1");
return true;
} catch (NumberFormatException ex) {
return false;
}
}
private static boolean surrogatesSupported() {
try {
Character.isHighSurrogate('a');
return true;
} catch (NoSuchMethodError ex) {
return false;
}
}
/**
* Report an error at the given position using the provided arguments.
*/
private void lexError(int pos, String key, Object... args) {
log.error(pos, key, args);
token = ERROR;
errPos = pos;
}
/**
* Report an error at the current token position using the provided
* arguments.
*/
private void lexError(String key, Object... args) {
lexError(pos, key, args);
}
/**
* Convert an ASCII digit from its base (8, 10, or 16)
* to its value.
*/
private int digit(int base) {
char c = ch;
int result = Character.digit(c, base);
if (result >= 0 && c > 0x7f) {
lexError(pos + 1, "illegal.nonascii.digit");
ch = "0123456789abcdef".charAt(result);
}
return result;
}
/**
* Convert unicode escape; bp points to initial '\' character
* (Spec 3.3).
*/
private void convertUnicode() {
if (ch == '\\' && unicodeConversionBp != bp) {
bp++;
ch = buf[bp];
if (ch == 'u') {
do {
bp++;
ch = buf[bp];
} while (ch == 'u');
int limit = bp + 3;
if (limit < buflen) {
int d = digit(16);
int code = d;
while (bp < limit && d >= 0) {
bp++;
ch = buf[bp];
d = digit(16);
code = (code << 4) + d;
}
if (d >= 0) {
ch = (char) code;
unicodeConversionBp = bp;
return;
}
}
lexError(bp, "illegal.unicode.esc");
} else {
bp--;
ch = '\\';
}
}
}
/**
* Read next character.
*/
// bp值加1，将ch更新为buf数组中保存的下一个待处理的字符
private void scanChar() {
ch = buf[++bp];
if (ch == '\\') {
convertUnicode();
}
}
/**
* Read next character in comment, skipping over double '\' characters.
*/
private void scanCommentChar() {
scanChar();
if (ch == '\\') {
if (buf[bp + 1] == '\\' && unicodeConversionBp != bp) {
bp++;
} else {
convertUnicode();
}
}
}
/**
* Append a character to sbuf.
*/
// sbuf扩容
private void putChar(char ch) {
if (sp == sbuf.length) {
char[] newsbuf = new char[sbuf.length * 2];
System.arraycopy(sbuf, 0, newsbuf, 0, sbuf.length);
sbuf = newsbuf;
}
sbuf[sp++] = ch;
}
/**
* Read next character in character or string literal and copy into sbuf.
*/
// 读取下一个字符或string文字，并且复制进sbuf
// 处理字符常量
private void scanLitChar() {
if (ch == '\\') { // 处理转义字符
if (buf[bp + 1] == '\\' && unicodeConversionBp != bp) {
bp++;
putChar('\\');
scanChar();
} else {
scanChar();
switch (ch) {
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
char leadch = ch;
int oct = digit(8);
scanChar();
if ('0' <= ch && ch <= '7') {
// 将八进制表示的数转换为十进制表示，然后强制转换为char类型后调用putChar()方法
oct = oct * 8 + digit(8);
scanChar();
if (leadch <= '3' && '0' <= ch && ch <= '7') {
oct = oct * 8 + digit(8);
scanChar();
}
}
putChar((char) oct);
break;
case 'b':
putChar('\b');
scanChar();
break;
case 't':
putChar('\t');
scanChar();
break;
case 'n':
putChar('\n');
scanChar();
break;
case 'f':
putChar('\f');
scanChar();
break;
case 'r':
putChar('\r');
scanChar();
break;
case '\'':
putChar('\'');
scanChar();
break;
case '\"':
putChar('\"');
scanChar();
break;
case '\\':
putChar('\\');
scanChar();
break;
default:
lexError(bp, "illegal.esc.char");
}
}
} else if (bp != buflen) {// 处理非转义字符
putChar(ch);
scanChar();
}
}
private void scanDigits(int digitRadix) {
char saveCh;
int savePos;
do {
if (ch != '_') {
putChar(ch);
} else {
if (!allowUnderscoresInLiterals) {
lexError("unsupported.underscore.lit", source.name);
allowUnderscoresInLiterals = true;
}
}
saveCh = ch;
savePos = bp;
scanChar();
} while (digit(digitRadix) >= 0 || ch == '_');
if (saveCh == '_') {
lexError(savePos, "illegal.underscore");
}
}
/**
* Read fractional part of hexadecimal floating point number.
*/
private void scanHexExponentAndSuffix() {
if (ch == 'p' || ch == 'P') {
putChar(ch);
scanChar();
skipIllegalUnderscores();
if (ch == '+' || ch == '-') {
putChar(ch);
scanChar();
}
skipIllegalUnderscores();
if ('0' <= ch && ch <= '9') {
scanDigits(10);
if (!allowHexFloats) {
lexError("unsupported.fp.lit", source.name);
allowHexFloats = true;
} else if (!hexFloatsWork) {
lexError("unsupported.cross.fp.lit");
}
} else {
lexError("malformed.fp.lit");
}
} else {
lexError("malformed.fp.lit");
}
if (ch == 'f' || ch == 'F') {
putChar(ch);
scanChar();
token = FLOATLITERAL;
} else {
if (ch == 'd' || ch == 'D') {
putChar(ch);
scanChar();
}
token = DOUBLELITERAL;
}
}
/**
* Read fractional part of floating point number.
*/
private void scanFraction() {
skipIllegalUnderscores();
if ('0' <= ch && ch <= '9') {
scanDigits(10);
}
int sp1 = sp;
if (ch == 'e' || ch == 'E') {
putChar(ch);
scanChar();
skipIllegalUnderscores();
if (ch == '+' || ch == '-') {
putChar(ch);
scanChar();
}
skipIllegalUnderscores();
if ('0' <= ch && ch <= '9') {
scanDigits(10);
return;
}
lexError("malformed.fp.lit");
sp = sp1;
}
}
/**
* Read fractional part and 'd' or 'f' suffix of floating point number.
*/
private void scanFractionAndSuffix() {
radix = 10;
scanFraction();
if (ch == 'f' || ch == 'F') {
putChar(ch);
scanChar();
token = FLOATLITERAL;
} else {
if (ch == 'd' || ch == 'D') {
putChar(ch);
scanChar();
}
token = DOUBLELITERAL;
}
}
/**
* Read fractional part and 'd' or 'f' suffix of floating point number.
*/
private void scanHexFractionAndSuffix(boolean seendigit) {
radix = 16;
Assert.check(ch == '.');
putChar(ch);
scanChar();
skipIllegalUnderscores();
if (digit(16) >= 0) {
seendigit = true;
scanDigits(16);
}
if (!seendigit) {
lexError("invalid.hex.number");
} else {
scanHexExponentAndSuffix();
}
}
private void skipIllegalUnderscores() {
if (ch == '_') {
lexError(bp, "illegal.underscore");
while (ch == '_') {
scanChar();
}
}
}
/**
* Read a number.
*
* @param radix The radix of the number; one of 2, j8, 10, 16.
*/
private void scanNumber(int radix) {
this.radix = radix;
// for octal, allow base-10 digit in case it's a float literal
int digitRadix = (radix == 8 ? 10 : radix);
boolean seendigit = false;
if (digit(digitRadix) >= 0) {
seendigit = true;
scanDigits(digitRadix);
}
if (radix == 16 && ch == '.') {
scanHexFractionAndSuffix(seendigit);
} else if (seendigit && radix == 16 && (ch == 'p' || ch == 'P')) {
scanHexExponentAndSuffix();
} else if (digitRadix == 10 && ch == '.') {
putChar(ch);
scanChar();
scanFractionAndSuffix();
} else if (digitRadix == 10 &&
(ch == 'e' || ch == 'E' ||
ch == 'f' || ch == 'F' ||
ch == 'd' || ch == 'D')) {
scanFractionAndSuffix();
} else {
if (ch == 'l' || ch == 'L') {
scanChar();
token = LONGLITERAL;
} else {
token = INTLITERAL;
}
}
}
/**
* Read an identifier.
*/
// 将所有组成标识符的字符从buf数组中读取出来按顺序存储到sbuf数组中，
// 最后作为参数调用names.fromChars()方法获取NameImpl对象方法
// 对字母、数字、下划线、美元符号及一些控制字符不做任何处理，
// 直接通过break跳出switch语句后重新执行do-while循环，
// 然后将这些字符存储到sbuf数组中，这都是标识符的一部分
private void scanIdent() {
boolean isJavaIdentifierPart;
char high;
do {
// sbuf数组不能存储更多字符，调用putChar()方法进行扩容
if (sp == sbuf.length) {
putChar(ch);
} else {
sbuf[sp++] = ch;
}
// optimization, was: putChar(ch);
scanChar();
switch (ch) {
case 'A':
case 'B':
case 'C':
case 'D':
case 'E':
case 'F':
case 'G':
case 'H':
case 'I':
case 'J':
case 'K':
case 'L':
case 'M':
case 'N':
case 'O':
case 'P':
case 'Q':
case 'R':
case 'S':
case 'T':
case 'U':
case 'V':
case 'W':
case 'X':
case 'Y':
case 'Z':
case 'a':
case 'b':
case 'c':
case 'd':
case 'e':
case 'f':
case 'g':
case 'h':
case 'i':
case 'j':
case 'k':
case 'l':
case 'm':
case 'n':
case 'o':
case 'p':
case 'q':
case 'r':
case 's':
case 't':
case 'u':
case 'v':
case 'w':
case 'x':
case 'y':
case 'z':
case '$':
case '_':
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
case '\u0000':
case '\u0001':
case '\u0002':
case '\u0003':
case '\u0004':
case '\u0005':
case '\u0006':
case '\u0007':
case '\u0008':
case '\u000E':
case '\u000F':
case '\u0010':
case '\u0011':
case '\u0012':
case '\u0013':
case '\u0014':
case '\u0015':
case '\u0016':
case '\u0017':
case '\u0018':
case '\u0019':
case '\u001B':
case '\u007F':
break;
case '\u001A': // EOI is also a legal identifier part
if (bp >= buflen) {// 已经没有待处理的字符了
name = names.fromChars(sbuf, 0, sp);
token = keywords.key(name);
return;
}
break;
default:
if (ch < '\u0080') {
// ch是ASCII编码中的一个字符
// 所有合法的ASCII字符已经在上面的case分支中进行了处理
isJavaIdentifierPart = false;
} else {
// 获取高代理项
high = scanSurrogates();
if (high != 0) {
if (sp == sbuf.length) {
putChar(high);
} else {
sbuf[sp++] = high;
}
// 方法会判断通过高代理项和低代理项表示的字符是否为合法
// 标识符的首字符
isJavaIdentifierPart = Character.isJavaIdentifierPart(
Character.toCodePoint(high, ch));
} else {
isJavaIdentifierPart = Character.isJavaIdentifierPart(ch);
}
}
// 生成Name和Token对象
if (!isJavaIdentifierPart) {
// 生成Name对象
name = names.fromChars(sbuf, 0, sp);
// 转化为Token对象
token = keywords.key(name);
return;
}
}
} while (true);
}
/**
* Scan surrogate pairs. If 'ch' is a high surrogate and
* the next character is a low surrogate, then put the low
* surrogate in 'ch', and return the high surrogate.
* otherwise, just return 0.
*/
private char scanSurrogates() {
if (surrogatesSupported && Character.isHighSurrogate(ch)) {
char high = ch;
scanChar();
if (Character.isLowSurrogate(ch)) {
return high;
}
ch = high;
}
return 0;
}
/**
* Return true if ch can be part of an operator.
*/
// 判断是否为标识符号或标识符号的一部分
private boolean isSpecial(char ch) {
switch (ch) {
case '!':
case '%':
case '&':
case '*':
case '?':
case '+':
case '-':
case ':':
case '<':
case '=':
case '>':
case '^':
case '|':
case '~':
case '@':
return true;
default:
return false;
}
}
/**
* Read longest possible sequence of special characters and convert
* to token.
*/
// 扫描出完整的标识符号
private void scanOperator() {
while (true) {
putChar(ch);
Name newname = names.fromChars(sbuf, 0, sp);
if (keywords.key(newname) == IDENTIFIER) {
sp--;
break;
}
name = newname;
token = keywords.key(newname);
scanChar();
if (!isSpecial(ch)) {
break;
}
}
}
/**
* Scan a documention comment; determine if a deprecated tag is present.
* Called once the initial /, * have been skipped, positioned at the second *
* (which is treated as the beginning of the first line).
* Stops positioned at the closing '/'.
*/
@SuppressWarnings("fallthrough")
private void scanDocComment() {
boolean deprecatedPrefix = false;
forEachLine:
while (bp < buflen) {
// Skip optional WhiteSpace at beginning of line
while (bp < buflen && (ch == ' ' || ch == '\t' || ch == FF)) {
scanCommentChar();
}
// Skip optional consecutive Stars
while (bp < buflen && ch == '*') {
scanCommentChar();
if (ch == '/') {
return;
}
}
// Skip optional WhiteSpace after Stars
while (bp < buflen && (ch == ' ' || ch == '\t' || ch == FF)) {
scanCommentChar();
}
deprecatedPrefix = false;
// At beginning of line in the JavaDoc sense.
if (bp < buflen && ch == '@' && !deprecatedFlag) {
scanCommentChar();
if (bp < buflen && ch == 'd') {
scanCommentChar();
if (bp < buflen && ch == 'e') {
scanCommentChar();
if (bp < buflen && ch == 'p') {
scanCommentChar();
if (bp < buflen && ch == 'r') {
scanCommentChar();
if (bp < buflen && ch == 'e') {
scanCommentChar();
if (bp < buflen && ch == 'c') {
scanCommentChar();
if (bp < buflen && ch == 'a') {
scanCommentChar();
if (bp < buflen && ch == 't') {
scanCommentChar();
if (bp < buflen && ch == 'e') {
scanCommentChar();
if (bp < buflen && ch == 'd') {
deprecatedPrefix = true;
scanCommentChar();
}
}
}
}
}
}
}
}
}
}
}
if (deprecatedPrefix && bp < buflen) {
if (Character.isWhitespace(ch)) {
deprecatedFlag = true;
} else if (ch == '*') {
scanCommentChar();
if (ch == '/') {
deprecatedFlag = true;
return;
}
}
}
// Skip rest of line
while (bp < buflen) {
switch (ch) {
case '*':
scanCommentChar();
if (ch == '/') {
return;
}
break;
case CR: // (Spec 3.4)
scanCommentChar();
if (ch != LF) {
continue forEachLine;
}
/* fall through to LF case */
case LF: // (Spec 3.4)
scanCommentChar();
continue forEachLine;
default:
scanCommentChar();
}
} // rest of line
} // forEachLine
return;
}
/**
* The value of a literal token, recorded as a string.
* For integers, leading 0x and 'l' suffixes are suppressed.
*/
@Override
public String stringVal() {
return new String(sbuf, 0, sp);
}
/**
* Read token.
*/
@Override
public void nextToken() {
try {
prevEndPos = endPos;
sp = 0;
while (true) {
pos = bp;
// switch语句会根据首个出现的字符来判断可能生成的Token对象
switch (ch) { // switch语句所有的处理分支可大概分为以下8类
/*
1、特殊字符的处理
2、标识符的处理
3、数字的处理
4、分隔符的处理
5、斜线作为首字符的处理
6、单引号作为首字符的处理
7、双引号作为首字符的处理
8、默认的处理
*/
// -------------------------------特殊字符的处理
// 这些字符都不会生成具体的Token对象，在当前的词法分析阶段调用scanChar()方法直接摒弃这些字符
case ' ': // (Spec 3.6) 空格
case '\t': // (Spec 3.6) 水平制表符
case FF: // (Spec 3.6) 换行换页符
// 将空格、水平制表符与换页符当作空白字符来处理
do {
scanChar();
} while (ch == ' ' || ch == '\t' || ch == FF);
endPos = bp;
processWhiteSpace();
break;
case LF: // (Spec 3.4) 换行符
scanChar();
endPos = bp;
processLineTerminator();
break;
case CR: // (Spec 3.4) 回车
scanChar();
if (ch == LF) { // 换行
scanChar();
}
endPos = bp;
processLineTerminator();
break;
// ----------------------------------特殊字符的处理
// ----------------------------------标识符的处理
case 'A':
case 'B':
case 'C':
case 'D':
case 'E':
case 'F':
case 'G':
case 'H':
case 'I':
case 'J':
case 'K':
case 'L':
case 'M':
case 'N':
case 'O':
case 'P':
case 'Q':
case 'R':
case 'S':
case 'T':
case 'U':
case 'V':
case 'W':
case 'X':
case 'Y':
case 'Z':
case 'a':
case 'b':
case 'c':
case 'd':
case 'e':
case 'f':
case 'g':
case 'h':
case 'i':
case 'j':
case 'k':
case 'l':