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);

Solution 1

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.

Solution 2

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.

Solution 3

• 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

Solution 4

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

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

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Comments

[denys]

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);

[Gilbert Le Blanc]

@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.

[Ciro Santilli OurBigBook.com]

On jdb there is locals.

[Anurag Awasthi]

BCEL hmm, ugly eh? I'd rather use dump(ar1, ar2m,..)