java--练习题

1、查找100以内质数

package practice;

public class zhishu {

	public static void main(String []args) {
		System.out.println("kaishi");
		long start = System.currentTimeMillis();
	/*
			for (int i =1;i<=1000;i++) {
				int issum= 0;
				for (int j=1;j<i;j++)
				{
					if (i%j==0)
					issum++;
				}
				if (issum ==1)
				System.out.println(i);
			
	
	}
			long end = System.currentTimeMillis();
			System.out.println(end-start);
	*/		
		
			for (int i =2;i<=100;i++) {
				int issum=1;
				for (int j=2;j<i;j++)
				{
					if (i%j==0)
					break;
					else
						issum=2;
				}
				
				if (issum ==2)
					System.out.println(i);
			
	
	}
			
			long end = System.currentTimeMillis();
			System.out.println(end-start);
			
			
	}
}

2、最大公约数、最小公倍数

package practice;
import java.util.Scanner;
public class fortest {
	
	public static void main(String []args) {
		Scanner sic = new Scanner(System.in);
		System.out.println("please inter num");
	    int m = sic.nextInt();
		System.out.println("please inter the other num");
	    int n = sic.nextInt();
	    int min = (m<=n)? m:n;
	    int max = (m>=n)? m:n;
	    for (int i =min;i>=1;i--) {
	    	if (m%i==0 && n%i==0) {
	    		System.out.println("zui da gong yue shu wei "+ i);
	    		break;
	    	}
	    }
	  
	    for (int j = max;;j++) {
	    	if (j%m==0 && j%n==0) {
	    		System.out.println("zui xiao gong yue shu wei "+j);
	    		break;
	    	}
	    }
	   
	    
	    
	}

}

3、计算狗多大

package practice;
import java.util.Scanner;
public class dogage {
	public static void main(String []args) {
		Scanner sic = new Scanner(System.in);
		System.out.println("please inter dog age");
	    int dog_age = sic.nextInt();
	    if (dog_age ==1 || dog_age==2) {
	    		System.out.println("dog age is" + dog_age*10.5);
	    }
	    else{
	    	int age_num=dog_age-2;
	    	dog_age=21+age_num*4;
	    	System.out.println("you dog age is "+dog_age);
	 	
	    }

	    
		
		
	}
	}