Java临阵磨枪(编程题)

alittlemc

发布于：2020年1月9日

输出char的Unicode值

public class E {
   public static void main(String args[]) {
     System.out.println((int)'你'); 
     System.out.println((int)'我');   
     System.out.println((int)'他');
   }
}

输出α到ω的字符

public class E {
   public static void main (String args[ ]) {
      char cStart='α',cEnd='ω';
      for(char c=cStart;c<=cEnd;c++)//char值++
        System.out.print(" "+c);//转为String
       
       //方法2
       char cStart0='α';
       for(int i=0;i<=24;i++)
        System.out.println(""+(char)(cStart0+i));
       //同理
       for(int i=0;i<=24;i++)
        System.out.println(""+(char)(945+i));
    }
    }
   }
}

求1!+2!+…+20!

public class Xiti1 {
  public static void main(String args[]) {
    long sum=0,a=1;
    int i=1;
      while(i<=20) {
          sum=sum+a;//主要目的
          i++;
          a=a*i;//一次循环一次自乘,求n!
      }
      System.out.println("sum="+sum);

      //推荐
      long sum1=0,a1=1;
          for(int j=1;j<=10;j++,a1*=j)
        	  sum1+=a1;
        	  
          System.out.println("sum="+sum1);
      
      
     long sum1=0;//配合函数计算,更加灵活但是效率降低
     	for(int j=1;j<=10;j++)
            sum1+=fun(j);
          		System.out.println("sum1="+sum1);

       }
    
    static int fun(int i) {
        return i>=2?fun(i-1)*i:1;
    }
}

求100内的素数

public class Xiti2 {
    public static boolean sushu(int i) {
        if(i<=2) return i==2:true?false;
        else {
            for(int j=3;j<=i;j+=2) {
                if(i%j==0)
                    break;
                else if(i==j)
                    return true;
                }
                return false;
        }
    }
  public static void main(String args[]) {
      for(j=2;j<=100;j++) 
          if(sushu(j))//是否是素数
              System.out.println(j);
   }
}

分别用do-while,for求1+1/2!+1/3!+…1/20!

class Xiti3 {
  public static void main(String args[]) {
      double sum=0,a=1,i=1;
      do {
          sum=sum+a;
           i++;
           a=(1.0/i)*a;
       }
       while(i<=20);
       System.out.println("使用do-while循环计算的sum="+sum);
//
       for(sum=0,i=1,a=1;i<=20;i++) {
          a=a*(1.0/i);
           sum=sum+a;
       }
       System.out.println("使用for循环计算的sum="+sum);
   }
}

1000内的完数

public class Xiti4 {
  public static void main(String args[]) {
     int sum=0,i,j;
     for(i=1;i<=1000;i++) {
        for(j=1,sum=0;j<i;j++) {
           if(i%j==0)
               sum+=j;
        }
        if(sum==i)
           System.out.println("完数:"+i);
     }
  }
}

for求8+88+888+…前10项

public class Xiti5 {
  public static void main(String args[]) {
     int m=8,item=m,i=1;
     long sum=0;
     for(i=1,sum=0,item=m;i<=10;i++) {
        sum=sum+item;
        item=item*10+m;
     }
     System.out.println(sum);
  }
}

求1+2+3+…+n<8888的最大正整数n

public class Xiti6 {
  public static void main(String args[]) {
      int n=1;
      long sum=0;
      while(true) {
        sum=sum+n;
        n++;
        if(sum>=8888) 
          break;
      }
      System.out.println("满足条件的最大整数:"+(n-1));
   }
}

类与对象

//CPU.java

public class CPU {
   int speed;  
   int getSpeed() {
      return speed;
   }
   public void setSpeed(int speed) {
      this.speed = speed; 
   }
}

//HardDisk.java

public class HardDisk {
   int amount;  
   int getAmount() {
      return amount;
   }
   public void setAmount(int amount) {
      this.amount = amount; 
   }
}

//PC.java

public class PC { 
    CPU cpu;
    HardDisk HD;
    void setCPU(CPU cpu) {
        this.cpu = cpu;
    }
     void setHardDisk(HardDisk HD) {
        this.HD = HD;
    }
    void show(){
       System.out.println("CPU速度:"+cpu.getSpeed());
       System.out.println("硬盘容量:"+HD.getAmount());
    }
}

//Test.java

public class Test {
   public static void main(String args[]) {
       CPU cpu = new CPU();
       HardDisk HD=new HardDisk();
       cpu.setSpeed(2200);
       HD.setAmount(200);
       PC pc =new PC();
       pc.setCPU(cpu);
       pc.setHardDisk(HD);
       pc.show();
    }
}

继承/接口

//Animal.java

public abstract class Animal {
    public abstract void cry();
    public abstract String getAnimalName();
}

//Simulator.java

public class Simulator {
   public void playSound(Animal animal) {
       System.out.print("现在播放"+animal.getAnimalName()+"类的声音:");
       animal.cry();
   }
}

//Dog.java

public class Dog extends Animal {
   public void cry() {
      System.out.println("汪汪...汪汪"); 
   }  
   public String getAnimalName() {
      return "狗";
   }
}

//Cat.java

public class Cat extends Animal {
   public void cry() {
      System.out.println("喵喵...喵喵"); 
   }  
   public String getAnimalName() {
      return "猫";
   }
}

//Application.java

public class Example5_13 {
   public static void main(String args[]) {
      Simulator simulator = new Simulator();
      simulator.playSound(new Dog());
      simulator.playSound(new Cat());
   }
}

//Animal.java

public interface Animal {
    public abstract void cry();
    public abstract String getAnimalName();
}

//Simulator.java

public class Simulator {
   public void playSound(Animal animal) {
       System.out.print("现在播放"+animal.getAnimalName()+"类的声音:");
       animal.cry();
   }
}

//Dog.java

public class Dog implements Animal {
   public void cry() {
      System.out.println("汪汪...汪汪"); 
   }  
   public String getAnimalName() {
      return "狗";
   }
}

//Cat.java

public class Cat implements Animal {
   public void cry() {
      System.out.println("喵喵...喵喵"); 
   }  
   public String getAnimalName() {
      return "猫";
   }
}

//Application.java

public class Example5_13 {
   public static void main(String args[]) {
      Simulator simulator = new Simulator();
      simulator.playSound(new Dog());
      simulator.playSound(new Cat());
   }
}

import java.util.*;
public class E {
    public static void main (String args[ ]){
      Scanner reader = new Scanner(System.in);
      double sum = 0;
       int m = 0;
       while(reader.hasNextDouble()){
           double x = reader.nextDouble();
           assert x< 100:"数据不合理";
           m = m+1;
           sum = sum+x;
       }
       System.out.printf("%d个数的和为%f\n",m,sum);
       System.out.printf("%d个数的平均值是%f\n",m,sum/m); 
    }
}

public class E {
  public static void main (String args[ ]) {
     String s1,s2,t1="ABCDabcd";
     s1=t1.toUpperCase();
     s2=t1.toLowerCase(); 
     System.out.println(s1);
     System.out.println(s2);
     String s3=s1.concat(s2);
      System.out.println(s3);
   }
}

public class E {
  public static void main (String args[ ]) {
     String s="ABCDabcd";
     char cStart=s.charAt(0);
     char cEnd = s.charAt(s.length()-1);
     System.out.println(cStart);
     System.out.println(cEnd);
   }
}

import java.util.*;
public class E {
  public static void main (String args[ ]) {
    int year1,month1,day1,year2,month2,day2;
      try{ year1=Integer.parseInt(args[0]);
           month1=Integer.parseInt(args[1]);
           day1=Integer.parseInt(args[2]);
           year2=Integer.parseInt(args[3]);
           month2=Integer.parseInt(args[4]);
           day2=Integer.parseInt(args[5]);
       }
       catch(NumberFormatException e)
         { year1=2012;
           month1=0;
           day1=1;
           year2=2018;
           month2=0;
           day2=1;
       } 
       Calendar calendar=Calendar.getInstance(); 
       calendar.set(year1,month1-1,day1);  
       long timeYear1=calendar.getTimeInMillis();
       calendar.set(year2,month2-1,day2);  
       long timeYear2=calendar.getTimeInMillis();
       long 相隔天数=Math.abs((timeYear1-timeYear2)/(1000*60*60*24));
       System.out.println(""+year1+"年"+month1+"月"+day1+"日和"+
                            year2+"年"+month2+"月"+day2+"日相隔"+相隔天数+"天");
   }
}

import java.util.*;
public class E {
  public static void main (String args[ ]) {
   double a=0,b=0,c=0;
      a=12;
      b=24;
      c=Math.asin(0.56);
      System.out.println(c);
      c=Math.cos(3.14);
      System.out.println(c);
      c=Math.exp(1);
      System.out.println(c);
      c=Math.log(8);
      System.out.println(c);
   }
}

public class E {
      public static void main (String args[ ]) {
        String str = "ab123you你是谁？";
        str = str.replaceAll(regex,"\\D+");//匹配一次或多次非数字
        System.out.println(str);
      }
}

import java.util.*;
public class E {
   public static void main(String args[]) {
      String cost = "数学87分，物理76分，英语96分";
      Scanner scanner = new Scanner(cost);
      scanner.useDelimiter("[^0123456789.]+");
      double sum=0;
      int count =0;
      while(scanner.hasNext()){
         try{  
             double score = scanner.nextDouble();
             count++;
             sum = sum+score;
             System.out.println(score);
         } 
         catch(InputMismatchException exp){
              String t = scanner.next();
         }   
      }
      System.out.println("总分:"+sum+"分");
      System.out.println("平均分:"+sum/count+"分");
   }
}

更新于：2020年1月9日

Java习题

Java临阵磨枪(全)

习题解答习题1（第1章）一、问答题 1．James Gosling 2．需3个步骤：用文本编辑器编写源文件。使用javac编译源文件,得到字节码文件。使用解释器运行程序。 ...

英语临阵磨枪

1. 谚语名言 When in Rome,do as the Romans入乡随俗每逢佳节倍思亲On festive occasions more than ever one misses o...