Java课程作业01

1.阶乘

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

public class CalculateN {

/**
* @param args
*/
public static void main(String[] args) {
System.out.print("请输入N：");
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.平方数的静方法

public class SquareInt {

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

for (int x = 1; x <= 10; x++) {
result = square(x);
// Math库中也提供了求平方数的方法
// result=(int)Math.pow(x,2);
System.out.println("The square of " + x + " is " + result + " ");
}
}

// 自定义求平方数的静态方法
public static int square(int y) {
return y * y;
}
}

3.随机数生产

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 += " ";
}

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

System.exit( 0 );
}
}

4.使用random类生产随机数

import java.util.Random;

public class TestSeed
{
public static void main(String[] args)
{
Random r1 = new Random(50);
System.out.println("第一个种子为50的Random对象");
System.out.println("r1.nextBoolean(): " + r1.nextBoolean());
System.out.println("r1.nextInt(): " + r1.nextInt());
System.out.println("r1.nextDouble(): " + r1.nextDouble());
System.out.println("r1.nextGaussian(): " + r1.nextGaussian());
System.out.println("---------------------------");

Random r2 = new Random(50);
System.out.println("第二个种子为50的Random对象");
System.out.println("r2.nextBoolean(): " + r2.nextBoolean());
System.out.println("r2.nextInt(): " + r2.nextInt());
System.out.println("r2.nextDouble(): " + r2.nextDouble());
System.out.println("r2.nextGaussian(): " + r2.nextGaussian());
System.out.println("---------------------------");

Random r3 = new Random(100);
System.out.println("种子为100的Random对象");
System.out.println("r3.nextBoolean(): " + r3.nextBoolean());
System.out.println("r3.nextInt(): " + r3.nextInt());
System.out.println("r3.nextDouble(): " + r3.nextDouble());
System.out.println("r3.nextGaussian(): " + r3.nextGaussian());


Random r4 = new Random(System.currentTimeMillis());
System.out.println("以当前时间为种子的Random对象");
System.out.println("r3.nextBoolean(): " + r4.nextBoolean());
System.out.println("r3.nextInt(): " + r4.nextInt());
System.out.println("r3.nextDouble(): " + r4.nextDouble());
System.out.println("r3.nextGaussian(): " + r4.nextGaussian());
}}

5.重载

public class MethodOverload {

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

6.CalculateN示例程序中的BUG

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

public class CalculateN {

/**
* @param args
*/
public static void main(String[] args) {
System.out.print("请输入N：");
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)));
}
}

由于计算机使用固定的位数来保存数值，因此，能处理的数值大小是有限的，当要处理的数值超过了这一范围时，计算机将会自动截断数值的二进制表示为它所能处理的最多位数，这将导致错误的处理结果。

7.比较两个浮点数

double i = 0.0001;

double j = 0.00010000000000000001;

 System.out.println(i==j); //输出：true

计算机不能精确地表达浮点数（特殊形式的除外），因此，当需要比较两个浮点数是否相等时，应该比较其差的绝对值是否在某个允许范围之内即可。

if ( Math.Abs(i - j) < 1e-10 )

System.out.println("true");

else

System.out.println("false");