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Scanner
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* 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).
*
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* 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
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package jdk.nashorn.internal.parser;
Utility for scanning thru a char array.
/**
* Utility for scanning thru a char array.
*
*/
public class Scanner {
Characters to scan. /** Characters to scan. */
protected final char[] content;
Position in content. /** Position in content. */
protected int position;
Scan limit. /** Scan limit. */
protected final int limit;
Current line number. /** Current line number. */
protected int line;
Current character in stream /** Current character in stream */
protected char ch0;
1 character lookahead /** 1 character lookahead */
protected char ch1;
2 character lookahead /** 2 character lookahead */
protected char ch2;
3 character lookahead /** 3 character lookahead */
protected char ch3;
Constructor
Params: - content – content to scan
- line – start line number
- start – position index in content where to start
- length – length of input
/**
* Constructor
*
* @param content content to scan
* @param line start line number
* @param start position index in content where to start
* @param length length of input
*/
protected Scanner(final char[] content, final int line, final int start, final int length) {
this.content = content;
this.position = start;
this.limit = start + length;
this.line = line;
reset(position);
}
Constructor
Scan content from beginning to end. Content given as a string
Params: - content – content to scan
/**
* Constructor
*
* Scan content from beginning to end. Content given as a string
*
* @param content content to scan
*/
protected Scanner(final String content) {
this(content.toCharArray(), 0, 0, content.length());
}
Copy constructor
Params: - scanner – scanner
- state – state, the state is a tuple {position, limit, line} only visible internally
/**
* Copy constructor
*
* @param scanner scanner
* @param state state, the state is a tuple {position, limit, line} only visible internally
*/
Scanner(final Scanner scanner, final State state) {
content = scanner.content;
position = state.position;
limit = state.limit;
line = state.line;
reset(position);
}
Information needed to restore previous state.
/**
* Information needed to restore previous state.
*/
static class State {
Position in content. /** Position in content. */
public final int position;
Scan limit. /** Scan limit. */
public int limit;
Current line number. /** Current line number. */
public final int line;
State(final int position, final int limit, final int line) {
this.position = position;
this.limit = limit;
this.line = line;
}
Change the limit for a new scanner.
Params: - limit – New limit.
/**
* Change the limit for a new scanner.
* @param limit New limit.
*/
void setLimit(final int limit) {
this.limit = limit;
}
boolean isEmpty() {
return position == limit;
}
}
Save the state of the scan.
Returns: Captured state.
/**
* Save the state of the scan.
* @return Captured state.
*/
State saveState() {
return new State(position, limit, line);
}
Restore the state of the scan.
Params: - state – Captured state.
/**
* Restore the state of the scan.
* @param state Captured state.
*/
void restoreState(final State state) {
position = state.position;
line = state.line;
reset(position);
}
Returns true of scanner is at end of input
Returns: true if no more input
/**
* Returns true of scanner is at end of input
* @return true if no more input
*/
protected final boolean atEOF() {
return position == limit;
}
Get the ith character from the content.
Params: - i – Index of character.
Returns: ith character or '\0' if beyond limit.
/**
* Get the ith character from the content.
* @param i Index of character.
* @return ith character or '\0' if beyond limit.
*/
protected final char charAt(final int i) {
// Get a character from the content, '\0' if beyond the end of file.
return i < limit ? content[i] : '\0';
}
Reset to a character position.
Params: - i – Position in content.
/**
* Reset to a character position.
* @param i Position in content.
*/
protected final void reset(final int i) {
ch0 = charAt(i);
ch1 = charAt(i + 1);
ch2 = charAt(i + 2);
ch3 = charAt(i + 3);
position = i < limit? i : limit;
}
Skip ahead a number of characters.
Params: - n – Number of characters to skip.
/**
* Skip ahead a number of characters.
* @param n Number of characters to skip.
*/
protected final void skip(final int n) {
if (n == 1 && !atEOF()) {
ch0 = ch1;
ch1 = ch2;
ch2 = ch3;
ch3 = charAt(position + 4);
position++;
} else if (n != 0) {
reset(position + n);
}
}
}