我有一个包含以下内容的文本文件：
0 12
1 15
2 6
3 4
4 3
5 6
6 12
7 8
8 8
9 9
10 13
我想从txt文件中读取这些整数，并将这两列保存到Java中的两个不同的数组中。
感谢 aioobe 为first part提供了很好的答案。
现在我想以这种方式开发它：
编写一个名为occurrence的方法，该方法将数字作为输入并写入该数字所具有的出现次数。
编写另一个名为occurrences的方法，该方法没有任何输入，但作为输出，它给出了文件中出现主要次数（在第二列中）的数字。
最后，Main程序会要求用户写一个1到3的数字。
1 = 方法，从输入数字（即第一列中的数字）中返回第二列中的相关数字。
2 = 第一个出现的方法（带输入的方法）
3 = 第二次出现的方法（没有输入的方法）
我编写了代码，但是有一些错误（关于将数组列表传递给方法），我需要你的帮助。 我是JAVA新手，所以如果您觉得代码不合适，请进行必要的更改。 这是我的最终代码：
import java.util.*; //importing some java classes
import java.lang.*;
import java.io.*;
public class list {
public static void main(String[] args) {
// Read the text file and store them into two arrays:
try {
List<Integer> column1 = new ArrayList<Integer>(); // Defining an integer Array List
List<Integer> column2 = new ArrayList<Integer>(); // Defining an integer Array List
Scanner myfile = new Scanner(new FileReader("c:/java/data.txt")); // Reading file using Scanner
while (myfile.hasNext()) { // Read file content using a while loop
column1.add(myfile.nextInt()); // Store the first integer into the first array list
column2.add(myfile.nextInt()); // Store the next integer into the second array list
}
myfile.close(); // close the file
System.out.println("column 1 elements are:\n" + column1); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
System.out.println("column 2 elements are:\n" + column2); // [12, 15, 6, 4, 3, 6, 12, 8, 8, 9, 13]
//Getting a number(1-3) from user:
Scanner cases = new Scanner(System.in);
System.out.println("Enter a number between 1-3: ");
int num = cases.nextInt();
switch (num) {
case 1:
Scanner case1 = new Scanner(System.in);
System.out.println("Enter a number from first column to see how many occurrences it has: ");
int numb = case1.nextInt();
System.out.println(column2.get(numb));
break;
case 2:
occurrence(column2.toArray());
break;
case 3:
occurrences(column2.toArray());
break;
default: System.out.println("the number is not 1 or 2 or 3!");
}
} catch (Exception e) { // we defined it just in the case of error
e.printStackTrace(); // shows the error
}
} // End of MAIN
public void occurrence(int[] arg) { // Defining occurrence method
int count = 0;
//Getting a number from user input:
Scanner userin = new Scanner(System.in);
System.out.println("Enter an integer number: ");
int number = userin.nextInt();
// Finding the occurrences:
for (int i = 0; i < arg.length; i++)
if (arg[i] == number) count++;
System.out.println( number + " is repeated " + count + " times in the second column.");
} // End of occurrence method
public void occurrences(int[] arg) { // Defining occurrenceS method
int max = 0;
// Finding the maximum occurrences:
for (int i = 1; i < arg.length; i++)
if (arg[i] > arg[max]) max = i;
System.out.println( max + " is the most repeated number." );
} // End of occurrenceS method
}
答案 0 :(得分：0)
您传递的是Object[]而您的方法需要int[]
（注意toArray（）返回一个Object []）
另外，occurrence()是实例方法，而main是静态的，您还需要将occurrence()更改为静态方法，或者创建列表实例。
所以方法签名将是：
public static void occurrences(Integer[] arg)
public static void occurrence(Integer[] arg)
和方法调用将是：
Integer[] temp = new Integer[column2.size()];
switch (num) {
case 1:
Scanner case1 = new Scanner(System.in);
System.out.println("Enter a number from first column to see how many occurrences it has: ");
int numb = case1.nextInt();
System.out.println(column2.get(numb));
break;
case 2:
occurrence(column2.toArray(temp));
break;
case 3:
occurrences(column2.toArray(temp));
break;
default: System.out.println("the number is not 1 or 2 or 3!");
}
P.S.这与你的问题无关，但是有一个强大的java约定，类名以大写字母开头。
答案 1 :(得分：0)
这是最终答案（我也更新了方法）：
import java.util.*; //By Mehdi Davoudi
import java.lang.*;
import java.io.*;
public class list {
public static void main(String[] args) {
// Read the text file and store them into two arrays:
try {
List<Integer> column1 = new ArrayList<Integer>(); // Defining an integer Array List
List<Integer> column2 = new ArrayList<Integer>(); // Defining an integer Array List
Scanner myfile = new Scanner(new FileReader("c:/java/data.txt")); // Reading file using Scanner
while (myfile.hasNext()) { // Read file content using a while loop
column1.add(myfile.nextInt()); // Store the first integer into the first array list
column2.add(myfile.nextInt()); // Store the next integer into the second array list
}
myfile.close(); // close the file
System.out.println("column 1 elements are:\n" + column1); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
System.out.println("column 2 elements are:\n" + column2); // [12, 15, 6, 4, 3, 6, 12, 8, 8, 9, 13]
//Getting a number(1-3) from user:
Scanner cases = new Scanner(System.in);
System.out.println("Enter a number between 1-3: ");
int num = cases.nextInt();
Integer[] temp = new Integer[column2.size()];
switch (num) {
case 1:
Scanner case1 = new Scanner(System.in);
System.out.println("Enter a number from first column to see its pair in second column: ");
int numb = case1.nextInt();
System.out.println(column2.get(numb));
break;
case 2:
Occurrence(column2.toArray(temp));
break;
case 3:
Occurrences(column2.toArray(temp));
break;
default: System.out.println("the number is not 1 or 2 or 3!");
}
} catch (Exception e) { // we defined it just in the case of error
e.printStackTrace(); // shows the error
}
} // End of MAIN
public static void Occurrence(Integer[] arg) { // Defining occurrence method
int count = 0;
//Getting a number from user input:
Scanner userin = new Scanner(System.in);
System.out.println("Enter an integer number: ");
int number = userin.nextInt();
// Finding the occurrences:
for (int i = 0; i < arg.length; i++)
if (arg[i] == number) count++;
System.out.println( number + " is repeated " + count + " times in the second column.");
} // End of occurrence method
public static void Occurrences(Integer[] ary) { // Defining occurrenceS method
// Finding the maximum occurrences:
Map<Integer, Integer> m = new HashMap<Integer, Integer>();
for (int a : ary) {
Integer freq = m.get(a);
m.put(a, (freq == null) ? 1 : freq + 1);
}
int max = -1;
int mostFrequent = -1;
for (Map.Entry<Integer, Integer> e : m.entrySet()) {
if (e.getValue() > max) {
mostFrequent = e.getKey();
max = e.getValue();
}
}
System.out.println( mostFrequent + " is the most repeated number in second column." );
} // End of occurrenceS method
}
答案 2 :(得分：-1)
我更喜欢BufferedReader。逐行读取它并使用String.split（）方法获取列元素。