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 9.2480Here 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;
}
}/** 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;
}
}/*
* 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);
}
}