java - 代码中获取java.lang.NumberFormatException

Question

代码:

我有 TriangleSummer 类，它有类变量

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)

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 行时得到 NumberFormatException，即第 4 行的值

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

.我完全不知道为什么？

Answer 1

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

好像最后还有空格。在传递给 Integer.parseInt(str);

之前执行 trim()