标准控制台读取工具
/****************************************************************************** * Copyright 2002-2015, Robert Sedgewick and Kevin Wayne. * * This file is part of algs4.jar, which accompanies the textbook * * Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne, * Addison-Wesley Professional, 2011, ISBN 0-321-57351-X. * http://algs4.cs.princeton.edu * * * algs4.jar is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * algs4.jar 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 for more details. * * You should have received a copy of the GNU General Public License * along with algs4.jar. If not, see http://www.gnu.org/licenses. ******************************************************************************/ //from N o w J a v a . c o m /****************************************************************************** * Compilation: javac StdIn.java * Execution: java StdIn (interactive test of basic functionality) * Dependencies: none * * Reads in data of various types from standard input. * ******************************************************************************/ package edu.pucit.cs.algo; import java.util.ArrayList; import java.util.InputMismatchException; import java.util.Locale; import java.util.NoSuchElementException; import java.util.Scanner; import java.util.regex.Pattern; /*时 代 J a v a 公 众 号 - nowjava.com 提供*/ /** * The <tt>StdIn</tt> class provides static methods for reading strings * and numbers from standard input. * These functions fall into one of four categories: * <p> * <ul> * <li>those for reading individual tokens from standard input, one at a time, * and converting each to a number, string, or boolean * <li>those for reading characters from standard input, one at a time * <li>those for reading lines from standard input, one at a time * <li>those for reading a sequence of values of the same type from standard input, * and returning the values in an array * </ul> * <p> * Generally, it is best not to mix functions from the different * categories in the same program. * <p> * <b>Reading tokens from standard input one at a time, * and converting to numbers and strings.</b> * You can use the following methods to read numbers, strings, and booleans * from standard input: * <ul> * <li> {@link #readInt()} * <li> {@link #readDouble()} * <li> {@link #readString()} * <li> {@link #readBoolean()} * <li> {@link #readShort()} * <li> {@link #readLong()} * <li> {@link #readFloat()} * <li> {@link #readByte()} * </ul> * <p> * Each method skips over any input that is whitespace. Then, it reads * the next token and attempts to convert it into a value of the specified * type. If it succeeds, it returns that value; otherwise, it * throws a {@link InputMismatchException}. * <p> * <em>Whitespace</em> includes spaces, tabs, and newlines; the full definition * is inherited from {@link Character#isWhitespace(char)}. * A <em>token</em> is a maximal sequence of non-whitespace characters. * The precise rules for describing which tokens can be converted to * integers and floating-point numbers are inherited from * <a href = "http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#number-syntax">Scanner</a>, * using the locale {@link Locale#US}; the rules * for floating-point numbers are slightly different * from those in {@link Double#valueOf(String)}, * but unlikely to be of concern to most programmers. * <p> * <b>Reading characters from standard input, one at a time.</b> * You can use the following two methods to read characters from standard input: * <ul> * <li> {@link #hasNextChar()} * <li> {@link #readChar()} * </ul> * <p> * The first method returns true if standard input has more input (including whitespace). * The second method reads and returns the next character of input on standard * input (possibly a whitespace character). * <p> * As an example, the following code fragment reads characters from standard input, * one character at a time, and prints it to standard output. * <pre> * while (!StdIn.hasNextChar()) { * char c = StdIn.readChar(); * StdOut.print(c); * } * </pre> * <p> * <b>Reading lines from standard input, one at a time.</b> * You can use the following two methods to read lines from standard input: * <ul> * <li> {@link #hasNextLine()} * <li> {@link #readLine()} * </ul> * <p> * The first method returns true if standard input has more input (including whitespace). * The second method reads and returns the remaining portion of * the next line of input on standard input (possibly whitespace), * discarding the trailing line separator. * <p> * A <em>line separator</em> is defined to be one of the following strings: * {@code \n} (Linux), {@code \r} (old Macintosh), * {@code \r\n} (Windows), * <code>\u2028</code>, <code>\u2029</code>, or <code>\u0085</code>. * <p> * As an example, the following code fragment reads text from standard input, * one line at a time, and prints it to standard output. * <pre> * while (!StdIn.hasNextLine()) { * String line = StdIn.readLine(); * StdOut.println(line); * } * </pre> * <p> * <b>Reading a sequence of values of the same type from standard input.</b> * You can use the following methods to read a sequence numbers, strings, * or booleans (all of the same type) from standard input: * <ul> * <li> {@link #readAllDoubles()} * <li> {@link #readAllInts()} * <li> {@link #readAllStrings()} * <li> {@link #readAllLines()} * <li> {@link #readAll()} * </ul> * <p> * The first three methods read of all of remaining token on standard input * and dconverts the tokens to values of * the specified type, as in the corresponding * {@code readDouble}, {@code readInt}, and {@code readString()} methods. * The {@code readAllLines()} method reads all remaining lines on standard * input and returns them as an array of strings. * The {@code readAll()} method reads all remaining input on standard * input and returns it as a string. * <p> * As an example, the following code fragment reads all of the remaining * tokens from standard input and returns them as an array of strings. * <pre> * String[] words = StdIn.readAllString(); * </pre> * <p> * <b>Differences with Scanner.</b> * {@code StdIn} and {@link Scanner} are both designed to parse * tokens and convert them to primitive types and strings. * Some of the main differences are summarized below: * <ul> * <li> {@code StdIn} is a set of static methods and reads * reads input from only standard input. It is suitable for use before * a programmer knows about objects. * See {@link In} for an object-oriented version that handles * input from files, URLs, * and sockets. * <li> {@code StdIn} uses whitespace as the delimiter between tokens. * <li> {@code StdIn} coerces the character-set encoding to UTF-8, * which is a standard character encoding for Unicode. * <li> {@code StdIn} coerces the locale to {@link Locale#US}, * for consistency with {@link StdOut}, {@link Double#parseDouble(String)}, * and floating-point literals. * <li> {@code StdIn} has convenient methods for reading a single * character; reading in sequences of integers, doubles, or strings; * and reading in all of the remaining input. * </ul> * <p> * Historical note: {@code StdIn} preceded {@code Scanner}; when * {@code Scanner} was introduced, this class was reimplemented to use it. * <p> * <b>Using standard input.</b> * Standard input is fundamental operating system abstraction, on Mac OS X, * Windows, and Linux. * The methods in {@code StdIn} are <em>blocking</em>, which means that they * will wait until you enter input on standard input. * If your program has a loop that repeats until standard input is empty, * you must signal that the input is finished. * To do so, depending on your operating system and IDE, * use either {@code <Ctrl-d>} or {@code <Ctrl-z>}, on its own line. * If you are redirecting standard input from a file, you will not need * to do anything to signal that the input is finished. * <p> * <b>Known bugs.</b> * Java's UTF-8 encoding does not recognize the optional * <a href = "http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4508058">byte-order mask</a>. * If the input begins with the optional byte-order mask, <tt>StdIn</tt> * will have an extra character <code>\uFEFF</code> at the beginning. * <p> * <b>Reference.</b> * For additional documentation, * see <a href="http://introcs.cs.princeton.edu/15inout">Section 1.5</a> of * <em>Introduction to Programming in Java: An Interdisciplinary Approach</em> * by Robert Sedgewick and Kevin Wayne. * * @author David Pritchard * @author Robert Sedgewick * @author Kevin Wayne */ public final class StdIn { /*** begin: section (1 of 2) of code duplicated from In to StdIn. */ // assume Unicode UTF-8 encoding private static final String CHARSET_NAME = "UTF-8"; // assume language = English, country = US for consistency with System.out. private static final Locale LOCALE = Locale.US; // the default token separator; we maintain the invariant that this value // is held by the scanner's delimiter between calls private static final Pattern WHITESPACE_PATTERN = Pattern .compile("\\p{javaWhitespace}+"); // makes whitespace significant private static final Pattern EMPTY_PATTERN = Pattern.compile(""); // used to read the entire input private static final Pattern EVERYTHING_PATTERN = Pattern .compile("\\A"); /*** end: section (1 of 2) of code duplicated from In to StdIn. */ private static Scanner scanner; // it doesn't make sense to instantiate this class private StdIn() { } //// begin: section (2 of 2) of code duplicated from In to StdIn, //// with all methods changed from "public" to "public static" /** * Returns true if standard input is empty (except possibly for whitespace). * Use this method to know whether the next call to {@link #readString()}, * {@link #readDouble()}, etc will succeed. * * @return <tt>true</tt> if standard input is empty (except possibly * for whitespace); <tt>false</tt> otherwise */ public static boolean isEmpty() { return !scanner.hasNext(); } /** * Returns true if standard input has a next line. * Use this method to know whether the * next call to {@link #readLine()} will succeed. * This method is functionally equivalent to {@link #hasNextChar()}. * * @return <tt>true</tt> if standard input is empty; * <tt>false</tt> otherwise */ public static boolean hasNextLine() { return scanner.hasNextLine(); } /** * Returns true if standard input has more inputy (including whitespace). * Use this method to know whether the next call to {@link #readChar()} will succeed. * This method is functionally equivalent to {@link #hasNextLine()}. * * @return <tt>true</tt> if standard input has more input (including whitespace); * <tt>false</tt> otherwise */ public static boolean hasNextChar() { scanner.useDelimiter(EMPTY_PATTERN); boolean result = scanner.hasNext(); scanner.useDelimiter(WHITESPACE_PATTERN); return result; } /** * Reads and returns the next line, excluding the line separator if present. * @return the next line, excluding the line separator if present */ public static String readLine() { String line; try { line = scanner.nextLine(); } catch (NoSuchElementException e) { line = null; } return line; } /** * Reads and returns the next character. * @return the next character */ public static char readChar() { scanner.useDelimiter(EMPTY_PATTERN); String ch = scanner.next(); assert ch.length() == 1 : "Internal (Std)In.readChar() error!" + " Please contact the authors."; scanner.useDelimiter(WHITESPACE_PATTERN); return ch.charAt(0); } /** * Reads and returns the remainder of the input, as a string. * @return the remainder of the input, as a string */ public static String readAll() { if (!scanner.hasNextLine()) return ""; String result = scanner.useDelimiter(EVERYTHING_PATTERN).next(); // not that important to reset delimeter, since now scanner is empty scanner.useDelimiter(WHITESPACE_PATTERN); // but let's do it anyway return result; } /** * Reads the next token and returns the <tt>String</tt>. * @return the next <tt>String</tt> */ public static String readString() { return scanner.next(); } /** * Reads the next token from standard input, parses it as an integer, and returns the integer. * @return the next integer on standard input * @throws InputMismatchException if the next token cannot be parsed as an <tt>int</tt> */ public static int readInt() { return scanner.nextInt(); } /** * Reads the next token from standard input, parses it as a double, and returns the double. * @return the next double on standard input * @throws InputMismatchException if the next token cannot be parsed as a <tt>double</tt> */ public static double readDouble() { return scanner.nextDouble(); } /** * Reads the next token from standard input, parses it as a float, and returns the float. * @return the next float on standard input * @throws InputMismatchException if the next token cannot be parsed as a <tt>float</tt> */ public static float readFloat() { return scanner.nextFloat(); } /** * Reads the next token from standard input, parses it as a long integer, and returns the long integer. * @return the next long integer on standard input * @throws InputMismatchException if the next token cannot be parsed as a <tt>long</tt> */ public static long readLong() { return scanner.nextLong(); } /** * Reads the next token from standard input, parses it as a short integer, and returns the short integer. * @return the next short integer on standard input * @throws InputMismatchException if the next token cannot be parsed as a <tt>short</tt> */ public static short readShort() { return scanner.nextShort(); } /** * Reads the next token from standard input, parses it as a byte, and returns the byte. * @return the next byte on standard input * @throws InputMismatchException if the next token cannot be parsed as a <tt>byte</tt> */ public static byte readByte() { return scanner.nextByte(); } /** * Reads the next token from standard input, parses it as a boolean, * and returns the boolean. * @return the next boolean on standard input * @throws InputMismatchException if the next token cannot be parsed as a <tt>boolean</tt>: * <tt>true</tt> or <tt>1</tt> for true, and <tt>false</tt> or <tt>0</tt> for false, * ignoring case */ public static boolean readBoolean() { String s = readString(); if (s.equalsIgnoreCase("true")) return true; if (s.equalsIgnoreCase("false")) return false; if (s.equals("1")) return true; if (s.equals("0")) return false; throw new InputMismatchException(); } /** * Reads all remaining tokens from standard input and returns them as an array of strings. * @return all remaining tokens on standard input, as an array of strings */ public static String[] readAllStrings() { // we could use readAll.trim().split(), but that's not consistent // because trim() uses characters 0x00..0x20 as whitespace String[] tokens = WHITESPACE_PATTERN.split(readAll()); if (tokens.length == 0 || tokens[0].length() > 0) return tokens; // don't include first token if it is leading whitespace String[] decapitokens = new String[tokens.length - 1]; for (int i = 0; i < tokens.length - 1; i++) decapitokens[i] = tokens[i + 1]; return decapitokens; } /** * Reads all remaining lines from standard input and returns them as an array of strings. * @return all remaining lines on standard input, as an array of strings */ public static String[] readAllLines() { ArrayList<String> lines = new ArrayList<String>(); while (hasNextLine()) { lines.add(readLine()); } return lines.toArray(new String[0]); } /** * Reads all remaining tokens from standard input, parses them as integers, and returns * them as an array of integers. * @return all remaining integers on standard input, as an array * @throws InputMismatchException if any token cannot be parsed as an <tt>int</tt> */ public static int[] readAllInts() { String[] fields = readAllStrings(); int[] vals = new int[fields.length]; for (int i = 0; i < fields.length; i++) vals[i] = Integer.parseInt(fields[i]); return vals; }