Java how to print all local variables?

Question

I have a method and want to examine variables inside it without debugging - is it possible in Java?

I do not want to write tons of code like:

System.out.println("a: " + a);

I want to something like:

System.out.printLocals();

Also it should be great to have something like:

System.out.printMembersOf(someObjectInstance);

All members has been asked at: http://stackoverflow.com/questions/1526826/printing-all-variables-value-from-a-class, let's keep this just for locals. — Ciro Santilli OurBigBook.com, Mar 05 '15 at 07:51

score 3 · Answer 1 · answered Mar 18 '11 at 16:45

3

Well, you can write a method with a varargs parameter and just write:

dump(variable1, variable2, variable3, variable4, ...);

It's not ideal, but it will be enough in some circumstances. There's no way to automatically grab all the local variables from a method and dump them though.

You might consider some sort of bytecode manipulation (e.g. with BCEL) which could do it... but it would be pretty ugly.

answered Mar 18 '11 at 16:45

Jon Skeet

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BCEL hmm, ugly eh? I'd rather use dump(ar1, ar2m,..) – Anurag Awasthi Aug 04 '17 at 18:12

score 3 · Answer 2 · answered Mar 18 '11 at 17:48

3

I want to have something like: System.out.printLocals();

Also it should be great to have something like: System.out.printMembersOf(someObjectInstance);

Just about every Java class has a toString method. You override that method, and you can get a string that represents what you're asking for.

Eclipse Helios, among other IDEs, will generate a basic toString method for you.

answered Mar 18 '11 at 17:48

Gilbert Le Blanc

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this will not work for case: `public void foo(int k, String s) { System.out.printLocals(); }` // expected output is the same as for `System.out.ptintln("k: " + Integer.toString(k)); System.out.ptintln("s: " + s);` – denys Mar 23 '11 at 12:44
@denys: You're correct. However, there's no reason you couldn't code a toLocalString method for each of the methods you wanted local variables. – Gilbert Le Blanc Mar 23 '11 at 12:59

score 1 · Answer 3 · answered Mar 18 '11 at 16:44

1

You can use System.out.println to print out variables. Example:

int i = 42;
System.out.println("i:" + i);

answered Mar 18 '11 at 16:44

dogbane

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gideon · Answer 4 · 2011-03-18T16:56:41.970

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Just print them out to the debugger. (Debugging with Eclipse)

OR

Print out to the console: (System.out.println("var"))

OR

User Log4J : http://en.wikipedia.org/wiki/Log4j

edited Mar 18 '11 at 16:56

answered Mar 18 '11 at 16:45

gideon

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On `jdb` there is `locals`. – Ciro Santilli OurBigBook.com Mar 05 '15 at 07:53

score 0 · Answer 5 · answered Mar 18 '11 at 16:43

0

What do you mean by "examining" ? Try a System.out.println(yourvariable), or (yourvariable.toString()) if it's an object. It'll display it in the console.

answered Mar 18 '11 at 16:43

Raveline

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score 0 · Answer 6 · answered Mar 18 '11 at 16:49

It's not simple to read the values of local variables at runtime, even if you're a debugger. If there are no debug symbols in your class, there is no way at all to see local variables, even if you use a debugger.

The most simple solution to see the values is printing them with System.out.println() or to use logging (slf4j).

If you want to example local variables at runtime without changing the code, you can try AOP (Aspect-oriented programming). Or you can use the same API that a debugger uses to examine the running VM.

Java how to print all local variables?

6 Answers6

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