I spent most of my time on bash terminal and looked for some command line javadoc tools, something like ruby or python interpreter's built in help system. I didn't found something good, so I build one for myself :). It is a great way to exploring the java API or any API generated using javadoc tools after some processing. You can search for packages, class, method, java docs, etc. It's support regular expression. You can apply nesting search like package:class:method means find some method on a class under this package. It's also highlight the search result and javadoc. Some example here. 

>> queue

Search result for : queue

 0: AbstractQueue                        8: LayoutQueue
 1: AbstractQueuedLongSynchronizer       9: LinkedBlockingQueue
 2: AbstractQueuedSynchronizer          10: PriorityBlockingQueue
 3: ArrayBlockingQueue                  11: PriorityQueue
 4: BlockingQueue                       12: Queue
 5: ConcurrentLinkedQueue               13: QueuedJobCount
 6: DelayQueue                          14: ReferenceQueue
 7: EventQueue                          15: SynchronousQueue

>> Math.sqrt

Help on sqrt

public static double sqrt(double a)

 Returns the correctly rounded positive square root of a double value.
 Special cases:

         * If the argument is NaN or less than zero, then the result is NaN.
         * If the argument is positive infinity, then the result is positive infinity.
         * If the argument is positive zero or negative zero, then the result is the same as the argument. Otherwise, the result is the double value closest to the true mathematical square root of the argument value.

 Parameters:

     a - a value.
 Returns:

     the positive square root of a. If the argument is NaN or less than zero, the result is NaN.

>> .runtime
 0: getRunTimeCodeBase       2: getRuntimeMXBean
 1: getRuntime



map   : search *map*  
M*p   : search M.*p  
m*p   : search m.*p  
0h    : help on 0th entry
j     : next
k     : previous
s     : say doc string
q     : quit
d     : class doc
package:class:method
:class : list class with package name 
return method on exact match
^----$ all class with length 4