问题
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);
回答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.
回答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.
回答3:
You can use System.out.println to print out variables. Example:
int i = 42;
System.out.println("i:" + i);
回答4:
- 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
回答5:
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.
回答6:
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.
来源：https://stackoverflow.com/questions/5355101/java-how-to-print-all-local-variables