Java设计实践课练习题

package hello;
import java.util.*;

public class Hello {
    public static void main(String args[]){
        double[] a = produce(10000);
        int[] b = tongJi(a);
        for (int e : b) {
            System.out.print(e +" ");
        }
        System.out.println();
        double exp = expect(a);
        System.out.println(exp);
        double f = fangCha(exp, a);
        System.out.println(f);
        
    }
    public static double[] produce(int length) {
        double[] a = new double[length];
        for (int i = 0; i < length; i++) {
            a[i] = Math.random() * 2 - 1;
        }
        return a;
    }
    public static int[] tongJi(double a[]) {
        int[] b = new int[20];
        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < b.length; j++) {
                if (a[i] > -1 + 0.1 * j && a[i] < -1 + 0.1 * (j + 1)) {
                    b[j]++;
                }
            }
        }
        return b;
    }
    public static double expect(double b[]) {
        double sum = 0;
        for (int i = 0; i < b.length; i++) {
            sum = sum + b[i];
        }
        double exp = sum/10000;
        return exp;
    }
    public static double fangCha(double exp, double a[]) {
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum = sum + (a[i] - exp) * (a[i] - exp);
        }
        double f = Math.sqrt(sum/10000);
        return f;
    }
}

package hello;
import java.util.*;

public class Hello {
    public static void main(String args[]){
        double[] a = produce(10000);
        int[] b = tongJi(a);
        for (int e : b) {
            System.out.print(e +" ");
        }
        System.out.println();
        double exp = expect(a);
        System.out.println(exp);
        double f = fangCha(exp, a);
        System.out.println(f);
        
    }
    public static double[] produce(int length) {
        double[] a = new double[length];
        for (int i = 0; i < length; i++) {
            a[i] = getNumRandom();
        }
        return a;
    }
    public static int[] tongJi(double a[]) {
        int[] b = new int[20];
        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < b.length; j++) {
                if (a[i] > -6 + 0.6 * j && a[i] < -6 + 0.6 * (j + 1)) {
                    b[j]++;
                }
            }
        }
        return b;
    }
    public static double expect(double b[]) {
        double sum = 0;
        for (int i = 0; i < b.length; i++) {
            sum = sum + b[i];
        }
        double exp = sum/10000;
        return exp;
    }
    public static double fangCha(double exp, double a[]) {
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum = sum + (a[i] - exp) * (a[i] - exp);
        }
        double f = Math.sqrt(sum/10000);
        return f;
    }
    public static double getNumRandom() {
        double sum = 0;
        for (int i = 0 ; i < 12; i++) {
            sum = sum + Math.random();
        }
        return sum - 6;
    }
}

 

import java.util.Scanner;

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        System.out.println("请输入第一个字符串数组：");
        Scanner input = new Scanner(System.in);
        String s1 = input.nextLine();
        System.out.println("请输入第二个字符串数组：");
        String s2 = input.nextLine();
        System.out.println("比较结果为："+compareMinus(s1, s2));
    }
    public static boolean compareMinus(String s1, String s2) {
        boolean flag = true;
        for (int i = 0; i < s1.length(); i++) {
            char ch = s1.charAt(i);
            if (ch == '-') {
                if (s2.charAt(i) != '-') {
                    flag = false;
                }
            }
        }
        return flag;
    }
}

 Java文件操作：

①文件删除与创建，文件存在则删除，不存在则创建

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

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        File file = new File("C:\Users\木子月月鸟\Desktop\file.txt");
        if (file.exists()) {
            file.delete();
            System.out.println("文件已经删除");
        } else {
            try {
                file.createNewFile();
                System.out.println("文件已经创建");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

②获取文件信息，名字，长度，是否隐藏等

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

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        File file = new File("C:\Users\木子月月鸟\Desktop\file.txt");
        if (file.exists()) {
            String name = file.getName();
            long length = file.length();
            boolean hidden = file.isHidden();
            System.out.println("文件名称是："+ name);
            System.out.println("文件长度是："+ length);
            System.out.println("该文件是隐藏文件么？"+ hidden);
        } else {
            System.out.println("该文件不存在！");
        }
    }
}

③用FileInputStream和FileOutputStream对文件进行读写操作

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

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        File file = new File("C:\Users\木子月月鸟\Desktop\file.txt");
        try {
            FileOutputStream out = new FileOutputStream(file);
            byte[] buy = "我有一只小毛驴，我从来也不骑".getBytes();
            out.write(buy);
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            FileInputStream in = new FileInputStream(file);
            byte[] by = new byte[1024];
            int len = in.read(by);
            System.out.println("文件中的信息是: "+new String(by, 0 ,len));
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

④用FileReader、FileWriter、BufferedReader、BufferedWriter对文件进行读写操作

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

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        File file = new File("C:\Users\木子月月鸟\Desktop\file.txt");
        String content[] = {"好久不见","最近好吗","常常联系"};
        try {
            FileWriter fileWriter = new FileWriter(file);
            BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
            for (int i = 0; i < content.length; i++) {
                bufferedWriter.write(content[i]);
                bufferedWriter.newLine();
            }
            bufferedWriter.close();
            fileWriter.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            FileReader fileReader = new FileReader(file);
            BufferedReader bufferedReader = new BufferedReader(fileReader);
            String string = null;
            int i = 0;
            while ((string = bufferedReader.readLine()) != null) {
                i++;
                System.out.println("第"+ i + "行:" + string);
            }
            bufferedReader.close();
            fileReader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

 ⑤用FileReader、FileWriter、BufferedReader、BufferedWriter对文件复制

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

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        File source = new File("C:\Users\木子月月鸟\Desktop\source.txt");
        File target = new File("C:\Users\木子月月鸟\Desktop\target.txt");
        try {
            FileReader fileReader = new FileReader(source);
            FileWriter fileWriter = new FileWriter(target);
            BufferedReader bufferedReader = new BufferedReader(fileReader);
            BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
            String string = null;
            while ((string = bufferedReader.readLine()) != null) {
                System.out.println(string);
                bufferedWriter.write(string);
                bufferedWriter.newLine();
            }
            bufferedReader.close();
            fileReader.close();
            bufferedWriter.close();
            fileWriter.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 ⑥文件压缩操作

import java.io.*;
import java.util.*;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

/**
 * Created by 木子月月鸟 on 2017/5/24.
 */
public class Test {
    public static void main(String[] args) {
        Test test = new Test();
        try {
            test.zip("C:\Users\木子月月鸟\Desktop\test.zip", new File("C:\Users\木子月月鸟\Desktop\test"));
            System.out.println("压缩完成!");
        }catch (Exception e) {
        }
    }
    private void zip(String zipFileName, File inputFile) throws Exception {
        ZipOutputStream out = new ZipOutputStream(new FileOutputStream(zipFileName));
        zip(out, inputFile, "");
        System.out.println("文件压缩中.....");
        out.close();
    }
    private void zip(ZipOutputStream out, File file, String base) throws Exception {
        if (file.isDirectory()) {
            File[] files = file.listFiles();
            out.putNextEntry(new ZipEntry(base + "/"));
            base = base.length() == 0 ? "" : base + "/";
            for (int i = 0; i < files.length; i++) {
                zip(out, files[i], base + files[i]);
            }
        } else {
            out.putNextEntry(new ZipEntry(base));
            FileInputStream in = new FileInputStream(file);
            int b;
            System.out.println(base);
            while ((b = in.read()) != -1) {
                out.write(b);
            }
            in.close();
        }
    }
}

（7）文件解压缩操作