Java习题作业

1. Write a complete program that prints numbers from 1 to 50, but if numbers that are multiples of 5, print HiFive, else if numbers that are divisible by 2, print HiTwo, and else if numbers that are divisible by 3 or 7, print HiThreeOrSeven.

public class Prints {
	public static void main(String[] args) {
		for (int i = 1;i <=50;i++) {
			if (i % 5 == 0) 
		        System.out.println("HiFive");
		      else if (i % 2 == 0)
		        System.out.println("HiTwo");
		      else if (i % 3 == 0 || i % 7 == 0)
		        System.out.println("HiThreeOrSeven");
		      else
		        System.out.println(i + " ");  
		}

	}

}

2.Write a loop that computes 100 / 1 + 99 / 2 + 98 / 3 + ... + 2 / 99 + 1 / 100.

public class LoopComputes {
	public static void main(String[] args) {
		double sum = 0;
		   
	    for (int i = 0; i <= 99; i++) {
	    	
	    	sum += (100.0 - i) / (i + 1.0);
	    }

	    System.out.println("Sum is " + sum);


	}

}

3. Write aprogram that counts the number of lowercase letters in a string. Your programshould prompt the user to enter the string and display the count.

import java.util.Scanner;
public class LowercaseCounts {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Please enter a string:");
		String str = input.next();

		int lowerNum = 0;
		for (int i = 0;i < str.length();i++) {
			if ((int)str.charAt(i) >= 97 && (int)str.charAt(i) <= 122) {
				lowerNum += 1;
			}
		}
		System.out.println("Lowercase counts:" + lowerNum);
	}
	
}

4.Write a method tocompute the following series:

m(i) = (1 / 3) + (2 / 5) + ... + (i / (2 * i +1))

i      m(i)
1    0.3333
2    0.7333
	.
	.
	.
19    8.7602
20    9.2480

Here is the outline of the program:

public class Test {
  public static void main(String[] args) {
    // Fill in the code here
    

  }

  public   double m(int i) {
    // Fill in the code here


  }
}

import java.util.*;
public class MethodCompute {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Please enter the number of items to be calculated:");
		int num = input.nextInt();

		double  sum =  MethodCompute.compute(num);

		System.out.println((int)(sum * 10000.0) / 10000.0);
	}
	
	private static double compute(int num) {
		double sum = 0.0;
		for (int i = 1;i <= num; i++) {
			sum += (double)i / (2.0 * i + 1.0);
		}
		return  sum;
	}
}

5.Implement the following method that returns a suffix ofan integer with a specified number of digits.

/** For example, getSuffix(12345, 2) returns 45 andgetSuffix(1234567, 3) returns 567

import java.util.*;
public class SpecifiedNumber {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Enter an integer and the number of bits required：");  // 输入一个整数和需要后几位数
		int num = input.nextInt();
		int count = input.nextInt();

		int number = SpecifiedNumber.getSuffix(num, count);
		System.out.println(number);

	}
	public static int getSuffix(int value, int numberOfDigits) {
		String str = String.valueOf(value);  //  整数转字符串
		String str1 = str.substring(str.length()-numberOfDigits,str.length());  //  截取后几个字符
		
		int i = Integer.parseInt(str1); //  截取到的字符串转整数
		return i;
	   }
}

6.Write a program that reads the integers between1 and 50 and counts the occurrences of each. Assume the input ends with 0.

/*
 * 计算小于等于50个整数之和，以0结束，输入一次回车一次
 */
import java.util.*;
public class IntegersSum {
	public static void main(String[] args) {
		int i = 1;
		int j = 0;
		int sum = 0;
		System.out.println("Calculation is less than the sum of 50 integers, with the end of 0, enter a carriage return once：");
		while (i != 0 && j < 50) {
			Scanner input = new Scanner(System.in);
			i = input.nextInt();
			sum += i;
			j++;
		}
		System.out.println(sum);
	}

}

7.Write a program that prompts the user to enter10 integers and displays all combinations of picking two numbers from 10.

import java.util.*;

import org.omg.CORBA.INTERNAL;
public class Combination {

	public static void main(String[] args) {
		int []num = new int[10];
		Scanner input = new Scanner(System.in);
		System.out.println("Please enter 10 integers：");

		for(int i =0; i<10;i++){
		  num[i]=input.nextInt();
		}
		for (int i = 0; i < 9;i++) {
			for (int j = 1;j < 10;j++) {
				System.out.println(num[i]+""+num[j] + " " +num[j]+""+num[i]);
			}
		}

	}

}

8.Write a method that returns a sorted string using thefollowing method:

Public staticString sort(String s){}

For example,sort(“acb”) returns abc

Write a testprogram that prompts the user to enter astring and displays the sorted string.

import java.util.*;
public class StringSort {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Please enter a string：");
		String str = input.next();
		
		String str1 = StringSort.sort(str);
		System.out.println("Sort after：" + str1);
	}
	public static String sort(String s){
		char[] arrayCh = s.toCharArray(); //  字符串转字符数组
		Arrays.sort(arrayCh);  // 利用数组帮助类自动排序
		 return new String(arrayCh);
	}

}

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