1.Java实现将九九乘法表输入到文本文件
public class Test1 {
public static void main(String[] args) throws FileNotFoundException {
System.setOut(new PrintStream("table99.txt"));//重定项屏幕输出到ps对象中
for (int i = 1; i < 10; i++) {
for (int j = 1; j <= i; j++) {
System.out.print(j + " * " + i + " = " + i * j +" ");
}
System.out.println();
}
}
}
2.从类似如下的文本文件中读取出所有的姓名，并打印出重复的姓名和重复的次数，
并按重复次数排序,如果次数相同按姓名字母排序：
1,zhangsan,28
2,lisi,35
3,zhangsan,28
4,wangwu,35
5,zhangsan,28
6,lisi,35
7,zhaoliu,28
8,tianqi,35
class NameBean implements Comparable<NameBean> {
// 名字
private String name;
// 出现次数
private Integer count;
public NameBean(String name, Integer count) {
super();
this.name = name;
this.count = count;
}
public String toString() {
return name + " 出现 " + count;
}
public int compareTo(NameBean bean) {
if (this.count > bean.count) {
return 1;
} else if (this.count < bean.count) {
return -1;
} else {
return this.name.compareTo(bean.name);
}
}
}
public class Test2 {
public static void readFile(File file) throws IOException {
Scanner sc = new Scanner(file);
Map<String, Integer> nameMap = new TreeMap<String, Integer>();
// 名字和重复次数的集合
Set<NameBean> nameSet = new TreeSet<NameBean>();
while (sc.hasNextLine()) {
String line = sc.nextLine();
String[] info = line.split(",");
String name = info[1];
if (nameMap.containsKey(name)) {
int count = nameMap.get(name);
nameMap.put(name, count + 1);
} else {
nameMap.put(name, 1);
}
}
Set<Map.Entry<String, Integer>> entrys = nameMap.entrySet();
Iterator<Map.Entry<String, Integer>> it = entrys.iterator();
while (it.hasNext()) {
Map.Entry<String, Integer> entry = it.next();
nameSet.add(new NameBean(entry.getKey(), entry.getValue() - 1));
}
System.out.println(nameSet);
}
public static void main(String[] args) throws IOException {
readFile(new File("student.txt"));
}
}
3.编写一个程序，将d:java目录下的所有.java文件复制到d:jad目录下，
并将原来文件的扩展名从.java改为.jad。
public class Test3 {
public static void copy(File src, File dest) throws IOException {
if (src == null || !src.exists()) {
System.out.println("源不存在");
return;
}
if (dest != null && !dest.exists()) {
dest.mkdir();
}
File[] fs = src.listFiles(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.endsWith(".java");
}
});
OutputStream out = null;
InputStream in = null;
for (File f : fs) {
String oldName = f.getName();
StringBuilder newName = new StringBuilder();
newName.append(oldName.substring(0, oldName.lastIndexOf('.'))).append(".jad");
in = new FileInputStream(f);
out = new FileOutputStream(dest.getPath() + File.separator
+ newName.toString());
byte[] buff = new byte[1024];
int len = 0;
while ((len = in.read(buff)) != -1) {
out.write(buff, 0, len);
}
out.close();
in.close();
}
}
public static void main(String[] args) throws IOException {
File src = new File("d:/java");
File dest = new File("d:/jad");
copy(src, dest);
}
}
4.从键盘读入一行字符串，这行字符串内容类似如下:"2,10,1,22,19,30";
输入升序排序或者降序排序，然后根据输入打印排序结果
public class Test4 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
sc.useDelimiter(" ");
Set<Integer> set = new TreeSet<Integer>(new Comparator<Integer>() {
public int compare(Integer o1, Integer o2) {
return o1.compareTo(o2) * -1;
}
});
while(sc.hasNextLine()){
set.clear();
String ele = sc.nextLine();
String[] arr = ele.split(",");
for (String s : arr) {
set.add(new Integer(s));
}
System.out.println("排序后= "+set);
}
}
}
5.删除一个目录（注意：要删除目录必须删除目录下的文件和子目录)
public class Test5 {
public static void delDir(File dir) {
if (dir == null || !dir.exists()) {
return;
}
if (dir.isFile()) {
dir.delete();
} else {
File[] fs = dir.listFiles();
for (File f : fs) {
delDir(f);
if (dir.list().length == 0) {// 空目录
dir.delete();
}
}
}
}
public static void main(String[] args) {
File dir = new File("D:/jad");
delDir(dir);
}
}
6.将一个文件中的内容倒序（不允许用第二个文件)
public class Test6 {
public static void reverse(String file) {
int total = 0;// 读取的总字节数
char[] buff = new char[30];
try (Reader in = new FileReader(file);) {
int len = 0;
while ((len = in.read(buff)) != -1) {
total += len;
}
} catch (Exception e) {
}
//==============
try (Writer out = new FileWriter(file);) {
for (int i = total - 1; i >= 0; i--) {
out.write(buff[i]);
}
} catch (Exception e) {
}
}
public static void main(String[] args) {
// start哥曾信佛但佛信曾哥end
reverse("out.txt");
}
}
7.public class GuessDemo {
/**
* 1.系统先一个生成[1,100]之间的随机数; 2.程序得到键盘录入的数据,要做检查
*/
public static void guess() {
Integer ran = new Random().nextInt(100) + 1;// [1,100]
System.out.println("随机数= " + ran);
Scanner sc = new Scanner(System.in);
while (sc.hasNextLine()) {
String input = sc.nextLine();
// 检查input是否由数字组成
if (!input.matches("\d+")) {
System.out.println("亲,请输入数字");
} else {
Integer num = new Integer(input);
if (num > 100 || num < 1) {
System.out.println("亲,请输入的[1,100]之间的数字");
} else {
// [1,100];
switch (num.compareTo(ran)) {
case 1:
// 此时num> ran
System.out.println("亲,你输入大了");
break;
case -1:
System.out.println("亲,你输入小了");
break;
default:
System.out.println("亲,恭喜你中奖了");
return;
}
}
}
}
}
public static void main(String[] args) {
guess();
}
}