Cannot check array[0].lengh variable in debugger

[barriern]

Hi everyone.

I have an issue when trying to debug a program that contains 2D array. If I try to put breakpoints checking for array[0].length, it fails with:

Breakpoint condition 'array[0].length > 0' error: Cannot evaluate because of compilation error(s): length cannot be resolved or is not a field.

After somme diggining, it seems that the debugger considers the array[0] object as a double:

Breakpoint condition 'array[0][0] == 0' error: Cannot evaluate because of compilation error(s): The type of the expression must be an array type but it resolved to double.

Do you have any idea on how to solve this?

Thanks

Nicolas

Environment

• Operating System: Ubuntu 22.04.3 LTS
• JDK version:

openjdk 19.0.2 2023-01-17
OpenJDK Runtime Environment (build 19.0.2+7-Ubuntu-0ubuntu322.04)
OpenJDK 64-Bit Server VM (build 19.0.2+7-Ubuntu-0ubuntu322.04, mixed mode, sharing)

• Visual Studio Code version:

Version: 1.81.1
Commit: 6c3e3dba23e8fadc360aed75ce363ba185c49794
Date: 2023-08-09T22:18:39.991Z
Electron: 22.3.18
ElectronBuildId: 22689846
Chromium: 108.0.5359.215
Node.js: 16.17.1
V8: 10.8.168.25-electron.0
OS: Linux x64 6.2.0-26-generic snap

• Java extension version: Java Extension Pack (v0.25.13)
• Java Debugger extension version: v0.53.0

Steps To Reproduce

1. Add in Watch array.length
2. Add in Watch array[0].length
3. Add coniditional breakpoint in line 15: array[0].length > 0

Current Result

Breakpoint condition 'array[0].length > 0' error: Cannot evaluate because of compilation error(s): length cannot be resolved or is not a field.

Expected Result

Debugger should stop on breakpoint without error

Files

Code source: TestDebugger.java.txt
Log file:
client.log.2023-08-24.txt

[barriern]

I just found a similar issue (#1244), which seems to be unresolved at this time.

[oarcher]

see #1244 (comment). The workaround might be to declare your array as double array[][] (not double[][] array).

[github-actions]

Hi Nicolas Barrier (@barriern), I'm an AI Support assistant here to help with your issue. While the team reviews your request, I wanted to provide some possible tips and documentation that might help you in the meantime.

The Java Debugger’s expression evaluator currently doesn’t support nested array indexing or the special .length field in conditional breakpoints or watches. Workarounds:

• Move the check into code and set a standard breakpoint:

  if (array[0].length > 0) {
      System.out.println("hit"); // breakpoint here
  }

• Assign array[0] to a local before your breakpoint, then watch row.length:

  double[] row = array[0];
  // set breakpoint here, then watch row.length

• Evaluate in the Debug Console in two steps:
  1. double[] row = array[0]
  2. row.length

References:

• Local expression evaluation limitations (Local variable values not shown #634):
  • Similar “cannot be resolved” errors when watching locals
  • Local variable values not shown #634

• General evaluation failures in watches (Sometimes connot evaluate because of compilation error #574):
  • .hashCode() and str.length() failing with compilation errors
  • Sometimes connot evaluate because of compilation error #574

Other references with low confidence

• Debug console expression support (Debug console not working properly #169): complex expressions and variable lookups sometimes fail
  Debug console not working properly #169

The team will respond to your issue shortly. I hope these suggestions are helpful in the meantime. If this comment helped you, please give it a 👍. If the suggestion was not helpful or incorrect, please give it a 👎. Your feedback helps us improve!