Java代码习题3

（P306T9.4)使用随机类Random。 创建种子是1000的Random对象，然后，产生0至100间的50个随机数。每行显示10个，用空格间隔且对齐。

package MyJavaWorkSpace;

import java.util.s;

import java.util.Random;

import java.util.Scanner;

public class MyJavaWorkSpace {

public static void main(String[] args) {

// TODO Auto-generated method stub

Random random1= new Random(1000);

for(int j=0;j<5;j++){

for(int i=0;i<10;i++){

System.out.print(String.format("%-4d ",random1.nextInt(100)));

}

System.out.print("\n");

}

}

}

（P306T9.6)设计一个名为StopWatch的类，包含私有成员startTime和endTime、一个无参构造方法，用当前时间初始化startTime、一个start方法，将当前时间赋给startTime、一个stop方法，将当前时间赋给endTime、一个名为getElapsedTime方法，返回以毫秒为单位的流逝时间。编程测量对100000个随机数进行排序所花费的时间。

package MyJavaWorkSpace;

import java.util.s;

import java.util.Random;

public class StopWatch {

private long startTime;

private long endTime;

public StopWatch(){

this.startTime=System.currentTimeMillis();

}

public void start(){

this.startTime=System.currentTimeMillis();

}

public void end(){

this.endTime=System.currentTimeMillis();

}

public long getElapsenTime(){

return endTime-startTime;

}

public long getEndTime(){

return endTime;

}

public long getStartTime(){

return startTime;

}

public void setStartTime(long startTime){

this.startTime=startTime;

}

public void setEndTime(long endTime){

this.endTime=endTime;

}

public static void main(String[] aregs){

StopWatch stopWatch= new StopWatch();

int[]arr=new int[100000];

for(int i=0;i<100000;i++){

arr[i]=(int)(Math.random()*100);

}

s.sort(arr);

stopWatch.end();

System.out.println("starttime:"+stopWatch.getStartTime());

System.out.println("endtime:"+stopWatch.getEndTime());

System.out.println("exe.time:"+stopWatch.getElapsenTime());

}

}

package MyJavaWorkSpace;

import java.util.s;

import java.util.Random;

public class StopWatch {

private long startTime;

private long endTime;

public StopWatch(){

this.startTime=System.currentTimeMillis();

}

public void start(){

this.startTime=System.currentTimeMillis();

}

public void end(){

this.endTime=System.currentTimeMillis();

}

public long getElapsenTime(){

return endTime-startTime;

}

public long getEndTime(){

return endTime;

}

public long getStartTime(){

return startTime;

}

public void setStartTime(long startTime){

this.startTime=startTime;

}

public void setEndTime(long endTime){

this.endTime=endTime;

}

public static void main(String[] aregs){

StopWatch stopWatch= new StopWatch();

int[]arr=new int[100000];

for(int i=0;i<100000;i++){

arr[i]=(int)(Math.random()*100);

}

s.sort(arr);

stopWatch.end();

System.out.println("The starttime is:");

long beginning=stopWatch.getStartTime();

showTime(beginning);

System.out.println("The endtime is:");

long ending=stopWatch.getEndTime();

showTime(ending);

System.out.println("exe.time:"+stopWatch.getElapsenTime());

}

public static void showTime(long totalMilliSeconds){

long currentMilliSeconds=totalMilliSeconds%1000;

long currentSecond1=totalMilliSeconds%100;

long totalSeconds=totalMilliSeconds/1000;//获取总秒数；

long currentSecond=totalSeconds%60;//获取当前秒数；

long totalMinutes=totalSeconds/60;//获取总分钟数；

long currentMinute=totalMinutes%60;//获取当前分钟数；

long totalHours=totalMinutes / 60;//获取总小时数；

long currentHour=totalHours % 24;//获取当前小时数；

if(currentHour==24)

currentHour=00;

else

currentHour=totalHours % 24;

System.out.println(currentHour+8+":"+currentMinute+":"+currentSecond+"."+currentSecond1+"."+currentMilliSeconds);

}

}

(P308T9.10)设计一个表示二次方程的QuadraticEquation类，

包括：

私有成员a,b,c；

一个参数为a,b,c的构造方法；

a,b,c的get方法；

计算判别式的getDiscriminant方法；

返回根的方法getRoot1和getRoot2.

编写程序，提示输入a,b,c的值，输出二次方程的根。

package MyJavaWorkSpace;

import java.util.s;

import java.util.Scanner;

public class QuadraticEquation {

private double a;

private double b;

private double c;

public void geta(){

Scanner intput1=new Scanner(System.in);

a=intput1.nextDouble();

}

public void getb(){

Scanner intput2=new Scanner(System.in);

b=intput2.nextDouble();

}

public void getc(){

Scanner intput3=new Scanner(System.in);

c=intput3.nextDouble();

}

public Double getDiscrimnant(){

return (b*b)-4*a*c;

}

public Double getRoot1(){

if(((b*b)-4*a*c)<0)

return 0.00;

else{

Double i;

i=(b*b)-4*a*c;

return ((-b-Math.sqrt(i))/(2*a));

}

}

public Double getR00t2(){

if(((b*b)-4*a*c)<0)

return 0.00;

else{

Double i;

i=(b*b)-4*a*c;

return ((-b+Math.sqrt(i))/(2*a));

}

}

public static void main(String[] aregs){

QuadraticEquation quadraticEquation= new QuadraticEquation();

System.out.println("please input the number of a,b,c.");

quadraticEquation.geta();

quadraticEquation.getb();

quadraticEquation.getc();

System.out.println("Discrimnant="+quadraticEquation.getDiscrimnant());

System.out.println("Root1="+quadraticEquation.getRoot1());

System.out.println("Root2="+quadraticEquation.getR00t2());

}

}

package MyJavaWorkSpace;

import java.util.s;

import java.util.Scanner;

public class QuadraticEquation {

private double a;

private double b;

private double c;

Scanner intput=new Scanner(System.in);

public void geta(){

a=intput.nextDouble();

}

public void getb(){

b=intput.nextDouble();

}

public void getc(){

c=intput.nextDouble();

}

public Double getDiscrimnant(){

return (b*b)-4*a*c;

}

public Double getRoot1(){

if(((b*b)-4*a*c)<0)

return 0.00;

else{

Double i;

i=(b*b)-4*a*c;

return ((-b-Math.sqrt(i))/(2*a));

}

}

public Double getR00t2(){

if(((b*b)-4*a*c)<0)

return 0.00;

else{

Double i;

i=(b*b)-4*a*c;

return ((-b+Math.sqrt(i))/(2*a));

}

}

public static void main(String[] aregs){

QuadraticEquation quadraticEquation= new QuadraticEquation();

System.out.println("please input the number of a,b,c.");

quadraticEquation.geta();

quadraticEquation.getb();

quadraticEquation.getc();

System.out.println("Discrimnant="+quadraticEquation.getDiscrimnant());

System.out.println("Root1="+quadraticEquation.getRoot1());

System.out.println("Root2="+quadraticEquation.getR00t2());

}

}

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