java - 为什么没有在正确的行上报告 NPE

Question

运行以下内容:

public class NPESample {

  String value;

  public static void main(String[] args) {
    NPESample npeSample = null;
    "foo"
        .replaceAll(
            "f",
            npeSample.value);
  }
}

会给:

Exception in thread "main" java.lang.NullPointerException
    at NPESample.main(NPESample.java:9)

报告的第 (7) 行是 "foo"而不是发生 NPE 的实际线路 (10) npeSample.value .
为什么是这样？我在调试代码时感到惊讶，并被代码中报告的“错误”行号所抛弃。
要重现运行这个:

cat > ./NPESample.java <<DELIM
public class NPESample {

  String value;

  public static void main(String[] args) {
    NPESample npeSample = null;
    "foo"
        .replaceAll(
            "f",
            npeSample.value);
  }
}
DELIM

javac NPESample.java
java NPESample

输出是:

Exception in thread "main" java.lang.NullPointerException
    at NPESample.main(NPESample.java:7)

javac -version
javac 13.0.1

java -version
openjdk version "13.0.1" 2019-10-15
OpenJDK Runtime Environment (build 13.0.1+9)
OpenJDK 64-Bit Server VM (build 13.0.1+9, mixed mode, sharing)

Answer 1

对我来说，这看起来不像是一个错误。具体来说，好像是自由映射不是一对一的，as the SPEC says :

That is, LineNumberTable attributes may together represent a given line of a source file, and need not be one-to-one with source lines.

偶 JDK-15报告错误的行:

Cannot read field "value" because "npeSample" is null

在线 9 .