Java语言程序设计-基础篇-第八版-第九章

package chapter9字符串和文本IO;

import java.util.Scanner;

public class PalindromeIgnoreNonAlphanumeric {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a string: ");
String s = input.nextLine();
System.out.println("Ignoring non-alphanumeric characters, \nis " + s
+ " a palindrome? " + isPalindrome(s));
}

public static boolean isPalindrome(String s) {
String s1 = filter(s);
String s2 = reverse(s1);
return s2.equals(s1);
}

public static String filter(String s) {
StringBuilder stringBuilder = new StringBuilder();

for (int i = 0; i < s.length(); i++) {
if (Character.isLetterOrDigit(s.charAt(i))) {
stringBuilder.append(s.charAt(i));
}
}
return stringBuilder.toString();
}

public static String reverse(String s) {
StringBuilder stringBuilder = new StringBuilder(s);
stringBuilder.reverse();
return stringBuilder.toString();
}
}

package chapter9字符串和文本IO;

import java.util.Scanner;

public class ReadData {
public static void main(String[] args) throws Exception {
java.io.File file = new java.io.File("scores.txt");
Scanner input = new Scanner(file);

while (input.hasNext()) {
String firstName = input.next();
String mi = input.next();
String lastName = input.next();
int score = input.nextInt();
System.out.println(firstName + " " + mi + " " + lastName + " "
+ score);
}
input.close();
}
}

package chapter9字符串和文本IO;
import java.util.Scanner;
import javax.swing.JFileChooser;
public class ReadFileUsingJFileChooser {
public static void main(String[] args) throws Exception {
JFileChooser fileChooser = new JFileChooser();

if (fileChooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
java.io.File file = fileChooser.getSelectedFile();
Scanner input = new Scanner(file);

while (input.hasNext()) {
System.out.println(input.nextLine());
}
input.close();
}
else {
System.out.println("No file selected");
}
}
}

package chapter9字符串和文本IO;

import java.io.*;
import java.util.*;

public class ReplaceText {
public static void main(String[] args) throws Exception {
if (args.length != 4) {
System.out
.println("Usage: java ReplaceText sourceFile targetFile oldStr newStr");
System.exit(0);
}

File sourceFile = new File(args[0]);
if (!sourceFile.exists()) {
System.out.println("Source file " + args[0] + " does not exist");
System.exit(0);
}

File targetFile = new File(args[1]);
if (targetFile.exists()) {
System.out.println("Target file " + args[1] + " already exists");
System.exit(0);
}

Scanner input = new Scanner(sourceFile);
PrintWriter output = new PrintWriter(targetFile);

while (input.hasNext()) {
String s1 = input.nextLine();
String s2 = s1.replaceAll(args[2], args[3]);
output.println(s2);
}

input.close();
output.close();
}
}

package chapter9字符串和文本IO;

public class TestFileClass {
public static void main(String[] args) {
java.io.File file = new java.io.File("image/baby.png");
System.out.println("Does it exist? " + file.exists());
System.out.println("The file has " + file.length() + " byters ");
System.out.println("Can it be read? " + file.canRead());
System.out.println("Can it be written? " + file.canWrite());
System.out.println("Is it a directory? " + file.isDirectory());
System.out.println("Is it a file? " + file.isFile());
System.out.println("Is it absolute? " + file.isAbsolute());
System.out.println("Is it hidden? " + file.isHidden());
System.out.println("Absolute path is " + file.getAbsolutePath());
System.out.println("Last modified on "
+ new java.util.Date(file.lastModified()));

}
}

package chapter9字符串和文本IO;

public class WriteData {
public static void main(String[] args) throws Exception {
java.io.File file = new java.io.File("scores.txt");
if (file.exists()) {
System.out.println("File already exists");
System.exit(0);
}
java.io.PrintWriter output = new java.io.PrintWriter(file);
output.print("John T Smith ");
output.println(90);
output.print("Eric K Jones ");
output.println(85);

output.close();
}
}

package chapter9字符串和文本IO;

import java.util.Scanner;

public class CountEachLetter {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a string: ");
String s = input.next();
int[] counts = countLetters(s.toLowerCase());
for (int i = 0; i < counts.length; i++) {
if (counts[i] != 0)
System.out.println((char) ('a' + i) + " appears  " + counts[i]
+ ((counts[i] == 1) ? " time" : " times"));
}
}

public static int[] countLetters(String s) {
int[] counts = new int[26];

for (int i = 0; i < s.length(); i++) {
if (Character.isLetter(s.charAt(i)))
counts[s.charAt(i) - 'a']++;
}
return counts;
}
}

package chapter9字符串和文本IO;
import java.util.Scanner;
public class HexToDecimalConversion {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a hex number: ");
String hex = input.nextLine();

System.out.println("The decimal value for hex number "
+ hex + " is " + hexToDecimal(hex.toUpperCase()));
}
public static int hexToDecimal(String hex) {
int decimalValue = 0;
for (int i = 0; i < hex.length(); i++) {
char hexChar = hex.charAt(i);
decimalValue = decimalValue * 16 + hexCharToDecimal(hexChar);
}
return decimalValue;
}
public static int hexCharToDecimal(char ch) {
if (ch >= 'a' && ch <= 'F')
return 10 + ch - 'A';
else
return ch - '0';
}
}

package chapter9字符串和文本IO;

public class Calculator {
public static void main(String[] args) {
if (args.length != 3) {
System.out
.println("Usage: java Calculator operand1 operator operand2");
System.exit(0);
}
int result = 0;
switch (args[1].charAt(0)) {
case '+':
result = Integer.parseInt(args[0]) + Integer.parseInt(args[2]);
break;
case '-':
result = Integer.parseInt(args[0]) - Integer.parseInt(args[2]);
break;
case '*':
result = Integer.parseInt(args[0]) * Integer.parseInt(args[2]);
break;
case '/':
result = Integer.parseInt(args[0]) / Integer.parseInt(args[2]);
break;
}
System.out.println(args[0] + ' ' + args[1] + ' ' + args[2] + " = "
+ result);
}
}

package chapter9字符串和文本IO;
import java.util.Scanner;
public class CheckPalindrome {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Enter a string: ");
String s = input.next();

if (isPalindrome(s))
System.out.println(s + " is a palindrome");
else
System.out.println(s + " is not a palindrome");
}
public static boolean isPalindrome(String s) {
int low = 0;
int high = s.length() - 1;

while (low < high) {
if (s.charAt(low) != s.charAt(high))
return false;

low++;
high--;
}
return true;
}
}