在代码中获取java.lang.NumberFormatException

Question

代码：

我有TriangleSummer个类，该类具有类变量

static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

我的主要功能是

public static void main(String args[]) throws IOException {
    int noOfTestCases = Integer.parseInt(reader.readLine());
    for(int i=0;i<noOfTestCases;i++){
        int noOfEntries = Integer.parseInt(reader.readLine());
        System.out.println(computeMaxSum(noOfEntries));
    }
}

我的computeMaxSum()方法的相关部分是

public static int computeMaxSum(int noOfEntries) throws IOException {

    int[][] triangle = new int[noOfEntries][noOfEntries];

    for(int j=0;j<noOfEntries;j++){
        int k=0;
        for(String str : reader.readLine().split(" ")){
            triangle[j][k] = Integer.parseInt(str);
            k++;
        }
    }
  //further logic nothing to do with I/O
 }

最后是堆栈跟踪是

Exception in thread "main" java.lang.NumberFormatException: For input string: "4 "
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:492)
    at java.lang.Integer.parseInt(Integer.java:527)
    at Matrices.TriangleSummer.main(TriangleSummer.java:17)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

用于输入

2
3
1
2 1
1 2 3
4 
1 
1 2 
4 1 2
2 3 1 1 

所以我在读取第6行，即第4行的值4时遇到了NumberFormatException

int noOfEntries = Integer.parseInt(reader.readLine());

。而且我完全不知道为什么？

Answer 1

 java.lang.NumberFormatException: For input string: "4 "

似乎末尾有空格。在传递到trim()]之前先执行Integer.parseInt(str);

Answer 2

使用String#trim()从字符串“ 4”中删除空格

Answer 3

此人将删除您的空格