Java技术 第一次作业

（一）学习总结

1.在java中通过Scanner类完成控制台的输入，查阅JDK帮助文档，Scanner类实现基本数据输入的方法是什么？
代码开头加一句

Import java.util;

构建Scanner类对象

Scanner in = new Scanner(System.in);

特别注意String类型，next()键入空格会结束输入，nextLine()不会

package shiyan;
import java.util.Scanner;
public class Shiyan{
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num = in.nextInt();
        System.out.println(num);
        float num1 = in.nextFloat();
        System.out.println(num1);
        double num2 = in.nextDouble();
        System.out.println(num2);
        String words = in.next();
        System.out.println(words);
        String words1 = in.nextLine();
        System.out.println(words1);
        }
}

2.Random类和Math类的random()方法都能产生随机数，这两种方式有什么区别，各有什么特点呢？

package shiyan;
public class Shiyan {

    public static void main(String[] args) {
        double a=Math.random()*100+1;
        System.out.println(a);
    }
}

math类的随机数，double类型产生一个1到100的小数

import java.util.Random;
public class Shiyan {
    public static void main(String[] args) {
        Random rand = new Random();
        int num=rand.nextInt(26)+54;
        System.out.println(num); //26~80
    }

random类开头加import java,util.Random;
rand.nextInt(26)表示0到26，
rand.nextInt(26)+54范围0~80
3.运行下列程序，结果是什么？查阅资料，分析为什么。

public class Test {
    public static void main(String args[]) {
        double a = 0.1;
        double b = 0.1;
        double c = 0.1;
        if((a + b + c) == 0.3){
            System.out.println("等于0.3");
        }else {
            System.out.println("不等于0.3");
        }
    }
}

package shiyan;
import java.math.BigDecimal;
import java.math.MathContext;
public class Shiyan{
    public static void main(String args[]) {
        BigDecimal a = new BigDecimal(0.1);
        BigDecimal b = new BigDecimal(0.1);
        BigDecimal c = new BigDecimal(0.1);
        if(a.add(b).add(c).round(new MathContext(1)).equals(new BigDecimal("0.3"))){
            System.out.println("等于0.3");
        }else {
            System.out.println("不等于0.3");
        }
    }
}

看书379页，对照格式，不会损失精度

package shiyan1;
import java.util.Random;
import java.util.Scanner;
public class Caijiage {
    public static void main(String[] args) {
        Random rand = new Random();
        int price=rand.nextInt(100);
        System.out.println("猜猜多少钱：");
        for(int i=10; i>=0; i-- )
        {
            Scanner in = new Scanner(System.in);
            int inputPrice = in.nextInt();
            if(i==0) {
                System.out.println("you have try 10 times , and the true price is "+price);
            }
            else if(inputPrice<price) {
                System.out.println("low");
                System.out.println("and you have "+ (i-1) +" chance");
            }else if(inputPrice>price) {
                System.out.println("high");
                System.out.println("and you have "+ (i-1) +" chance");
            }else {
                System.out.println("true");
                System.out.println("you have try "+(10-i+1)+" times , and the true price is "+price);
                break;
            }
        }
    }

}

package shiyan1;
/*
 * 输出万年历
 * 设定1900.01.01为起点
    1970~1979
    1970 4
    1971 5
    1972 0
    1973 1
    1974 2
    1975 3
    1976 5
    1977 6
    1978 0
    1979 1
 */
import java.util.Scanner;
public class Wannianli {
    static boolean isLeap(int year){ //判断闰年
        if(year%400==0 || (year%4==0 && year%100!=0)){ //是闰年
            return true;
        }  

        else{
            return false;
        }
    }
    static final int N = 1900; //用N表示起始年份
    public static void main(String[] args){
        int n = 1;//1900年1月1日 是星期一
        int month[] = {0,31,28,31,30,31,30,31,31,30,31,30,31}; //用来存储月份的天数
        int year[] = new int[1001];  //用来存储每年1月1日是星期几
        year[0] = n;
        for(int i=1;i<year.length;i++){
            int days = 365;
            if(isLeap(i+N-1)){//如果它的前一年是闰年则需要加366
                days = 366;
                year[i] = (year[i-1] + days)%7;
            }
            else{
                year[i] = (year[i-1] + days)%7;
            }
        }
        /*
        for(int i=0;i<10;i++){
            System.out.println(year[i]);
        }
        */
        int Month ,Year;
        Scanner in = new Scanner(System.in);
        System.out.println("请输入年份在(1900~2900之间):");
        Year = in.nextInt();
        if(Year>2900 || Year<1900){
            System.out.println("输入年份不合法,请重新输入!");
            return;
        }
        //System.out.println(year[Year-1970]);
        System.out.println("请输入月份(1~12之间):");
        Month = in.nextInt();
        if(Month>12 || Month<1){
            System.out.println("输入月份不合法,请重新输入!");
            return;
        }
        System.out.println(" 星期日     " +"  星期一     "+"  星期二    "+"  星期三     "+"  星期四     "+"  星期五     "+"  星期六   ");
        System.out.println();
        if(isLeap(Year)){ //如果是闰年,2月改为29号
            month[2] = 29;
        }
        int day=0; //用来记录当前月的一号是今年的第几天
        for(int i=1;i<Month;i++){
            day = day + month[i];
        }  

        day = (year[Year-N]+day)%7;
        for(int i=0;i<7;i++){//输出控制
            if(day == i){
                System.out.print("  " + 1 + "   ");
                if(day == 6){
                    System.out.println();
                }
                break;
            }
            else{
                System.out.print("      ");
            }
        }
        for(int i=2;i<=month[Month];i++){
            if(i<10){
                System.out.print("  " + i + "   ");
            }
            else{
                System.out.print(" " + i + "   ");
            }
            if((day+i-1)%7 == 6){
                System.out.println();
            }
        }
    }
}

gitbash文件夹找不到了，明天继续弄，