我在开始新的编程课之前尝试使用Java进行练习。为此,我决定重新制作我从早期课程中制作的旧Perl程序。原始Perl文件输入用户输入的数字到数组中,并以四种方式输出数组:输入的数字,升序,降序,以及最大和最小的数字。
我在这里和其他地方通过几个例子查看了故障排除,当程序编译时,输出是错误的。这样,阵列输出了几十次,只输出输入的数字。我认为我的四个循环设置错误,但我还在学习Java,所以我可能错过了一些东西。这是现在的Java代码:
import java.util.ArrayList;
import java.util.Scanner;
public class ArrayOutPut {
static Scanner input = new Scanner(System.in);
static String convertToString(ArrayList<Integer> numbers) {
StringBuilder builder = new StringBuilder();
for (int i : numbers) {
builder.append(numbers);
builder.append(",");
}
builder.setLength(builder.length() - 1);
return builder.toString();
}
public static void main(String args[]) {
ArrayList<Integer> numbers = new ArrayList<Integer>();
int userInput;
int Largest = 0, Smallest = 0;
System.out.print(
"This program takes a set of integers from the user, and then outputs the results to the screen in four ways:\n");
System.out.print(
"the order they were entered seperated by a comma and a space, in ascending order, in descending order, and as Largest:Smallest.\n\n");
// explain to the user what the program does, needs, etc.
System.out.print("Please enter a number or -1 to end: ");
userInput = input.nextInt();
while (userInput != -1) {
System.out.print("Please enter a number or -1 to end: ");
numbers.add(userInput);
userInput = input.nextInt();
}
// Prints the array contents as entered
String sort = convertToString(numbers);
System.out.println(sort);
// prints numbers ascending
for (int i = 0; i < numbers.size(); i++) {
System.out.println(sort);
}
// prints numbers descending, largest first
for (int i = numbers.size() - 1; i >= 0; i--) {
System.out.println(sort);
}
for (int i = 0; i < numbers.size(); i++) {
int number = numbers.get(i);
if (i < Smallest) {
Smallest = i;
}
if (i > Largest) {
Largest = i;
}
System.out.println(Largest + Smallest);
}
}
}
有关其他参考,请参阅原始Perl程序:
#!/usr/bin/perl
use Modern::Perl;
my (@numbers, $userInput);# declare the array and more than one variable at a time
print("\nThis program takes a set of integers from the user, and
\nthen outputs the results to the screen in four ways:
\nthe ordered they were entered seperated by a comma and a space,
\nin ascending order, in descending order, and as Largest:Smallest.\n\n"); # explain to the user what is does, needs, etc
print "Please enter a number or -1 to end: ";
chomp ($userInput = <>); #loop is primed
if ($userInput == -1) {
say "\nThere's no numbers to process.\n";
}
else{
while($userInput != -1) {
push (@numbers, $userInput);
#Push the variable $userInput into @numbers.
print "Please enter a number or -1 to end: ";
chomp ($userInput = <>);
}
}
#Don't declare the @numbers array again, otherwise that'll clear out the entered numbers.
$" = ", ";
print "@numbers\n";
my @upsorted = sort {$a <=> $b} @numbers;
#prints numbers ascending, smallest first.
#Don't use $a, $b, or any number as a variable because they're reserved.
$" = ", ";
print "@upsorted\n";
my @downsorted = sort {$b <=> $a} @numbers;
#prints numbers descending, largest first
$" = ", ";
print "@downsorted\n";
print "$downsorted[0]:$upsorted[0]\n";
#must be set off with a blank line above and below
##End of program
好的,作为一个快速更新,我在查找tutorialspoint.com上的比较器后终于得到了运行程序。这是代码现在的位置:
import java.util.*;
public class ArrayOutPut {
static String convertToString(ArrayList<Integer> numbers) {
StringBuilder builder = new StringBuilder();
for (int i : numbers){
builder.append(i);
builder.append(",");
}
builder.setLength(builder.length() - 1);
return builder.toString();
}
public static void main(String args[]){
Scanner input = new Scanner(System.in);
ArrayList<Integer> numbers = new ArrayList<Integer>();
int userInput, largest = Integer.MIN_VALUE, smallest = Integer.MAX_VALUE;
System.out.println("This program takes a set of integers from the user, and then "
+ "outputs the results to the screen in four ways:");
System.out.println("the order they were entered seperated by a comma and a space, "
+ "in ascending order, in descending order, and as Largest:Smallest.");
System.out.println();
System.out.print("This program takes a set of integers from the user, and then outputs the results to the screen in four ways:\n");
System.out.print("the order they were entered seperated by a comma and a space, in ascending order, in descending order, and as Largest:Smallest.\n\n");
//explain to the user what the program does, needs, etc.
do {
System.out.print("Please enter a number or -1 to end: ");
userInput = input.nextInt();
if (userInput != -1) {
numbers.add(userInput);
largest = Math.max(largest, userInput);
smallest = Math.min(smallest, userInput);
}
} while (userInput != -1);
//Prints the array contents as entered
String sort = convertToString(numbers);
Comparator cmp = Collections.reverseOrder();
System.out.println(sort);
Collections.sort(numbers);
System.out.println(convertToString(numbers));
Collections.sort(numbers, Comparator.reverseOrder());
System.out.println(convertToString(numbers));
System.out.printf("Smallest = %d, Largest = %d%n", smallest, largest);
}
}
我唯一担心的是,当我编译时,我得到一个说明,该程序使用未经检查或不安全的操作,并且我应该使用-Xlint重新编译:未选中以获取详细信息。
答案 0 :(得分:1)
首先,如果使用Java 8+,我会在StringJoiner
1
convertToString
static String convertToString(List<Integer> numbers) {
StringJoiner sj = new StringJoiner(",");
numbers.stream().map(String::valueOf).forEach(sj::add);
return sj.toString();
}
其次,您需要sort
并再次致电convertToString
以打印结果。首选具有小写名称的变量。您可以使用内置函数消除循环。在将userInput
添加到-1
之前,请检查List
是否do-while
。我更喜欢public static void main(String args[]) {
Scanner input = new Scanner(System.in);
List<Integer> numbers = new ArrayList<>();
int userInput, largest = Integer.MIN_VALUE, smallest = Integer.MAX_VALUE;
System.out.println("This program takes a set of integers from the user, and then "
+ "outputs the results to the screen in four ways:");
System.out.println("the order they were entered seperated by a comma and a space, "
+ "in ascending order, in descending order, and as Largest:Smallest.");
System.out.println();
// explain to the user what the program does, needs, etc.
do {
System.out.print("Please enter a number or -1 to end: ");
userInput = input.nextInt();
if (userInput != -1) {
numbers.add(userInput);
largest = Math.max(largest, userInput);
smallest = Math.min(smallest, userInput);
}
} while (userInput != -1);
// Prints the array contents as entered
String sort = convertToString(numbers);
System.out.println(sort);
Collections.sort(numbers);
System.out.println(convertToString(numbers));
Collections.sort(numbers, Comparator.reverseOrder());
System.out.println(convertToString(numbers));
System.out.printf("Smallest = %d, Largest = %d%n", smallest, largest);
}
。像,
Comparator
根据您的编辑,您使用的是Java 7(不是Java 8+)。在这种情况下,您的代码(很高兴听到它正在工作),可以&#34;纠正&#34;使用类型 Comparator<Integer> cmp = Collections.<Integer> reverseOrder();
。像,
Integer
这将以反向顺序为您提供基于Comparator
的{{1}}。但是,也可以创建自定义 Comparator
。如,
Comparator<Integer> cmp = new Comparator<Integer>() {
@Override
public int compare(Integer o1, Integer o2) {
if (o1 == null) {
return (o2 == null) ? 0 : -1;
}
return o1.compareTo(o2);
}
};
然后你可以使用它(和反转它),如
System.out.println(sort);
Collections.sort(numbers, cmp);
System.out.println(convertToString(numbers));
Collections.sort(numbers, cmp.reversed());
System.out.println(convertToString(numbers));
1 并且,请更喜欢List
具体类型的ArrayList
界面。
答案 1 :(得分:1)
由于您已经在使用java.util
包的数据结构,因此我可以建议一种简单的方法来排序ArrayList
中的元素。如果numbers
是ArrayList
持有所有要处理的数字,请执行以下操作:
显示ArrayList numbers
中的数字,因为它们是
制作TreeSet
numbers
。 TreeSet
按升序自动对其元素进行排序注意:TreeSet仅包含唯一元素。因此,如果列表中的元素重复,它们将被删除。每个元素的只有一个副本将存储在Set中。
重新初始化numbers
,作为由numbers
构成的TreeSet。这是因为TreeSet只能以一个顺序显示。现在,显示numbers
的元素从头到尾按升序排列,从最后一个到第一个按降序排列。
最后,将numbers
的第一个和最后一个元素分别显示为最小和最大的数字。
这是一个代码。
import java.util.*;
class MyClass{
public static void main(String[] args){
ArrayList<Integer> numbers <--- holds all the numbers
System.out.println("The numbers are:");
for(int i=0; i<numbers.size();i++)
System.out.print(numbers.get(i).intValue()+" ");
TreeSet<Integer> ts = new TreeSet<Integer>(numbers);
numbers = new ArrayList<Integer>(ts);
System.out.println("\nThe numbers in ascending order are:");
for(int i=0;i<numbers.size();i++)
System.out.print(numbers.get(i).intValue()+" ");
System.out.println("\nThe numbers in descending order are:");
for(int i=numbers.size()-1;i>=0;i--)
System.out.print(numbers.get(i).intValue()+" ");
System.out.println("\nThe smallest number is "+numbers.get(0).intValue());
System.out.println("The largest number is "+numbers.get(numbers.size()-1).intValue());
}
}
我使用包含元素1 2 5 6 7
的ArrayList测试了它,这里是输出:
The numbers are:
7 5 6 1 2
The numbers in ascending order are:
1 2 5 6 7
The numbers in descending order are:
7 6 5 2 1
The smallest number is 1
The largest number is 7
我希望这会有所帮助。