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is there a way to write a Java method like toString in Javascript which if called on a method prints the source code of the method?

Sorry if this is a trivial question, so if this has already been asked, please direct me to the question.
I know that the tostring method in javascript, if called on a function will print the source code (more about it: link). Is it possible to do the same thing in Java?
So if I have the following identity function definition:
public class class1 {
int f1(int x){
return x;
}
}
And the following main function:
class Main {
public static void main(String args[]) {
class1 c1 = new class1();
????
}
}
Is there anything I can put in place of '????' that would print something like
int f1(int x){
return x;
}

Disclaimer: I'm not an expert at Java, or any programming language for that matter. However, I do know how to find information online.
This concept does not seem very doable within Java. To start:
JavaScript is an interpreted language, not a compiled language. A program such as C++ or Java needs to be compiled before it is run. The source code is passed through a program called a compiler, which translates it into bytecode that the machine understands and can execute. In contrast, JavaScript has no compilation step. Instead, an interpreter in the browser reads over the JavaScript code, interprets each line, and runs it. More modern browsers use a technology known as Just-In-Time (JIT) compilation, which compiles JavaScript to executable bytecode just as it is about to run.
Basically, JavaScript has the advantage of reading directly from the file with the source code, and executing it on the fly. Compiled languages such as Java won't have that sort of functionality built in by default for many reasons, including security. An application should be able to run without allowing hackers access to its source code as much as possible.
There have been attempts at doing various forms of what you're interested in, but the two easiest methods seem to be
Printing the original .java file line by line
Storing a string reference to the entire code or the method(s) required.
It also seems possible to print the method name, but not the body.
Aside from that, the only thing you might be able to get from a compiled, running java program, is bytecode, which would require a decompiler to have any hope of understanding the source behind it.
You can continue reading up on it through a few of the links here:
How do I print the method body reflectively?
Save a method into a variable, java 8
View a method's implementation (method body) using Java Reflection

Probably yes, but not a trivial one with a ready command. JavaScript is an interpreted language where the executing environment has access to the source code in its original form. That is how you can inspect it in a browser console and see the same variable names as are in the source code.
While the compiled/interpreted distinction is fuzzy for Java, it is definitely modified before execution. The bytecode used by Java's Just-in-Time compilation may be more readable than a fully compiled binary file, it is not the source. If the running program does not have access to the source code, it is less able to output it. A debugger running in an IDE can reference problems in the source; otherwise, you are limited to debugging the bytecodes.
This is why Keno Clayton suggested the question on Quine programs, which are meant to reproduce themselves. This answer outputs the source code by hard-coding it as a class attribute. You could take a similar approach with a pre-compilation script that went through all the methods and made strings out of their sources, but the result would be bulky and potentially sensitive.

How to debug javascript implementation In V8

I'm learning v8 now, but I have encountered some problems.
How to set a breakpoint a method's start address in memory if I want to debug a method's C++ implementation.
e.g. var a= new Array(0,1); a.indexOf(1) ; I want to set a breakpoint at slice's beginning, or are there other ways to track the assembler code ?
There are a lot of functions will be complied and writed into a file named snapshot.bin. so I can't set a breakpoint at the beginning of these functions.

You need to check the source code and find the implementation of slice. Then set a gdb/lldb break point in that .cc file: byiltins-typedarray.cc
A lot of functions are defined as builtin or runtime functions.

It depends on the kind of function you want to inspect.
You can compile without snapshot to get around snapshot-related debugging difficulties (at the cost of making startup quite a bit slower: several seconds in Debug mode).
You can modify the respective code generator to emit a break instruction at the beginning of the function. For the example of Array.indexOf, that's probably the easiest solution; the CodeStubAssembler instruction is called DebugBreak().
You can break somewhere else using GDB, find your way to the function in question (e.g. via isolate->builtins), and set a breakpoint on the address of its entry. (This requires a bit of V8 knowledge and/or code reading skills, but it's not difficult.)
You can use various --print-*-code flags to print code to stdout (without breaking on it).

JSCOMPILER_PRESERVE after compiling javascript with KJSCompiler

After compiling my JavaScript source with KJSCompiler (https://github.com/knyga/kjscompiler) I get this weird function wrapped around my code. If I try to include it in my live source code I get this error in the console "Uncaught ReferenceError: JSCOMPILER_PRESERVE is not defined ".
I thought that this problem occurred because I didn't add the "wrapper" in the JSON file of kjscompiler. After trying that it still occurs.
Does anyone have an idea how to fix this?

I came across this when using Closure Compiler directly via the Java API.
It seems to be caused by running the compiler in checks-only mode but with protect hidden side effects enabled. The late pass to remove protection of hidden side effects is skipped in checks-only mode.
I'm not sure about KJSCompiler specifically, but it might help to look at changing the compilation level to SIMPLE or ADVANCED, and/or how you might be able to control what checks and optimisations run to KJSCompiler, e.g. turning off CompilerOptions.protectHiddenSideEffects.
See https://github.com/google/closure-compiler/issues/1875

In addition to Steve S's answer:
set protectHiddenSideEffects after setting optimization level, as options.setProtectHiddenSideEffects(false); didn't work for me for GCC version v20180204 if I set it before setting CompilationLevel.
CompilationLevel.ADVANCED_OPTIMIZATIONS.setOptionsForCompilationLevel(compilerOptions);
//To remove JSCOMPILER_PRESERVE error: https://github.com/google/closure-compiler/issues/1875
compilerOptions.setProtectHiddenSideEffects(false);

Does Javascript compile or two-pass interpret?

I'm an admitted novice JavaScript programmer and am attempting to learn more. So I turn to you folks for help, with this easy question :). The O'Reilly book that I'm reading keeps referring to the compile-time of the JavaScript code. My knowledge of functional programming (scheme and the likes) tells me that the JavaScript is actually interpreted by the browser, most likely requiring two passes through the JavaScript.
Am I incorrect in my assessment? Or is the compile-time that the book references actually just the first pass of the interpreter, similar to how Perl or Python would function? Thanks!

It is browser-dependent. Look up WebKit's SquirrelFish Extreme and Google V8 to see what's at the fastest end of things, and look at Mozilla's JaegerMonkey for that implementation.
AFIAK V8 and SFX are JITs, so they compile JS code to native. JaegerMonkey and TraceMonkey combine in Firefox to form a system where if code would be faster traced, TraceMonkey executes it, and if code were faster native, JaegerMonkey compiles it, just like SFX.

Do you have a sentence that you could quote to help with context?
Javascript is compiled at the browser (it's sent to the browser in plain source). But it only gets compiled as it is loaded. So if you have a script tag followed by a div tag followed by a script tag then it will load those things sequentially. The browser will stop loading the entire page (it still downloads resources, just doesn't load HTML) until your script has been loaded (this is because the script may have 'document.write' within it).
<script>
var someVariable = 'hello world';
alert(document.getElementById('someid')); //alerts undefined
</script>
<div id='someid'></div>
<script>
alert(document.getElementById('someid')); //alerts 'someid'
alert(someVariable); //alerts 'hello world'
</script>

There's read-time and run-time in JS (as I like to think of it, since it's not really compiled, but interpreted). It sounds like the O'Reilly book is using compile-time as a synonym for read-time.
Read-time is when the engine reads all of the code and evaluates everything at the global scope. Usually this sets up hooks on events that will trigger code execution.
Run-time is everything else.

How do I add my own JavaScript libs to ClojureScript?

I want to write a Google Chrome extension, using ClojureScript. With ClojureScript I can use all the Google Closure libs, but afaik access to the Chrome browser is not included in those libs. So I want to wrap all the Chrome stuff in my own JavaScript lib.
So far I tried creating my own jar that has a single JavaScript file that just creates a Foo object and exports the constructor. I'v added this jar to the lib directory of the ClojureScript compiler (which also has for example goog.jar), but so far without luck:
Exception in thread "main" java.lang.IllegalArgumentException: No implementation of method: :-compile of protocol: #'cljs.closure/Compilable found for class: nil
at clojure.core$_cache_protocol_fn.invoke(core_deftype.clj:494)
at cljs.closure$eval1056$fn__1057$G__1047__1064.invoke(closure.clj:187)
at cljs.closure$get_compiled_cljs.invoke(closure.clj:422)
at cljs.closure$cljs_dependencies.invoke(closure.clj:440)
at cljs.closure$add_dependencies.doInvoke(closure.clj:462)
at clojure.lang.RestFn.applyTo(RestFn.java:139)
at clojure.core$apply.invoke(core.clj:602)
at cljs.closure$build.invoke(closure.clj:701)
at user$eval1246.invoke(cljsc.clj:21)
at clojure.lang.Compiler.eval(Compiler.java:6406)
at clojure.lang.Compiler.load(Compiler.java:6843)
at clojure.lang.Compiler.loadFile(Compiler.java:6804)
at clojure.main$load_script.invoke(main.clj:282)
at clojure.main$script_opt.invoke(main.clj:342)
at clojure.main$main.doInvoke(main.clj:426)
at clojure.lang.RestFn.invoke(RestFn.java:421)
at clojure.lang.Var.invoke(Var.java:405)
at clojure.lang.AFn.applyToHelper(AFn.java:163)
at clojure.lang.Var.applyTo(Var.java:518)
at clojure.main.main(main.java:37)
Has anyone tried this before?

Take a look at this post from Luke Vanderhart: "Using JavaScript libraries in ClojureScript"
http://lukevanderhart.com/2011/09/30/using-javascript-and-clojurescript.html
Also, this video from Kevin Lynagh: "Extending JavaScript Libraries from ClojureScript"
http://www.youtube.com/watch?v=XfzXFWTT-z0

If I remember Rich Hickeys talk correctly the whole program optimization of the closure compiler needs any library code to adhere to certain coding conventions. I think he also said something of JQuery not doing this but Dojo doing this. I never did this but you might find some useful information here