软工第二周作业

一、求平均数

（1）源码

public class SquareInt {

    public static void main(String[] args) {
        int result;

        for (int x = 1; x <= 10; x++) {
            result = square(x);
             9             // result=(int)Math.pow(x,2);
            System.out.println("The square of " + x + " is " + result + "\n");
        }
    }

    
    public static int square(int y) {
        return y * y;
    }
}

（2）运行结果

 

二、生成随机数

（1）源码

// RandomInt.java
// Shifted, scaled random integers
import javax.swing.JOptionPane;

public class RandomInt {
   public static void main( String args[] )
   {
      int value;
      String output = "";

      for ( int i = 1; i <= 20; i++ ) {
         value = 1 + (int) ( Math.random() * 6 );
         output += value + "  ";
         
         if ( i % 5 == 0 )
            output += "\n";
      }

      JOptionPane.showMessageDialog( null, output,
         "20 Random Numbers from 1 to 6",
         JOptionPane.INFORMATION_MESSAGE );

      System.exit( 0 );
   }
}

（2）运行结果

 三、使用Random类生成随机数

（1）源码

import java.util.*;

public class TestRandom
{
    public static void main(String[] args) 
    {
        Random rand = new Random();
        System.out.println("rand.nextBoolean()" + rand.nextBoolean());
        byte[] buffer = new byte[16];
        rand.nextBytes(buffer);
        System.out.println(Arrays.toString(buffer));
        
        System.out.println("rand.nextDouble()" + rand.nextDouble());
        
        System.out.println("rand.nextFloat()" + rand.nextFloat());
        /
        System.out.println("rand.nextGaussian()" + rand.nextGaussian());
        //
        System.out.println("rand.nextInt()" + rand.nextInt());
        
        System.out.println("rand.nextInt(26)" + rand.nextInt(26));
        //
        System.out.println("rand.nextLong()" +  rand.nextLong());
    }
}

（2）运行结果

 四、随机数应用案例

（1）

// RollDie.java
// Roll a six-sided die 6000 times
import javax.swing.*;

public class RollDie {
   public static void main( String args[] )
   {
      int frequency1 = 0, frequency2 = 0,
          frequency3 = 0, frequency4 = 0,
          frequency5 = 0, frequency6 = 0, face;
   
      // summarize results
      for ( int roll = 1; roll <= 6000; roll++ ) {
         face = 1 + (int) ( Math.random() * 6 );
   
         switch ( face ) {
            case 1:
               ++frequency1;
               break;
            case 2:
               ++frequency2;
               break;
            case 3:
               ++frequency3;
               break;
            case 4:
               ++frequency4;
               break;
            case 5:
               ++frequency5;
               break;
            case 6:
               ++frequency6;
               break;
         }
      }

      JTextArea outputArea = new JTextArea( 7, 10 );

      outputArea.setText(
         "Face\tFrequency" +
         "\n1\t" + frequency1 +
         "\n2\t" + frequency2 +
         "\n3\t" + frequency3 +
         "\n4\t" + frequency4 +
         "\n5\t" + frequency5 +
         "\n6\t" + frequency6 );

      JOptionPane.showMessageDialog( null, outputArea,
         "Rolling a Die 6000 Times",
         JOptionPane.INFORMATION_MESSAGE );
      System.exit( 0 );
   }
}

（2）运行结果

 五、参数可变的方法

（1）源码

import java.awt.*;
import java.awt.event.*;
import java.util.*;


public class VariableArgumentsTest{
    
    public static double max(double...values)
    {
        double largest=Double.MIN_VALUE;
        for (double v:values)
            if(v>largest) largest=v;
        return largest;
    }

    public static void main(String args[]) {
    
         System.out.println("Max:"+max(1,11,300,2,3));
            
    }
}

（2）运行结果

 

六、函数重载

（1）源码

// MethodOverload.java
// Using overloaded methods

public class MethodOverload {

    public static void main(String[] args) {
        System.out.println("The square of integer 7 is " + square(7));
        System.out.println("\nThe square of double 7.5 is " + square(7.5));
    }

    public static int square(int x) {
        return x * x;
    }

    public static double square(double y) {
        return y * y;
    }
}

（2）运行结果

 

（3）总结

①有重载的方法会根据传入数据的类型来选择不同的方法

②方法重载条件

1.方法名相同

2.参数类型不同，参数个数不同，或者是参数类型的顺序不同

七、递归求n的阶乘

（1）源码

import java.math.BigInteger;
import java.util.Scanner;


public class CalculateN {

    /**
     * @param args
     */
    public static void main(String[] args) {
        
        Scanner scanner=new Scanner(System.in);
        int number=scanner.nextInt();
        System.out.println(number+"!="+calculateN2(number));
        
    }
    
    public static long calculateN(int n) {
        if(n==1 || n==0){
            return 1;
        }
        
        return n*calculateN(n-1);
    }

    public static BigInteger calculateN2(int n) {
        if(n==1 || n==0){
            return BigInteger.valueOf(1);
        }
        return BigInteger.valueOf(n).multiply(calculateN2((n-1)));
    }
}

（2）运行结果