#parameter passing

Passing HashMap from Java to Java Nashorn

Java Nashorn is the JavaScript engine shipped since Java 8. You can therefore use JavaScript wherever you have at least Java 8. Java 8 also has a standalone interpreter, called jjs.

It is possible to create a Java HashMap and use this structure directly in JavaScript. Here is the code:

import java.util.*; import java.io.*; import javax.script.*; public class HashMapDemo { public static void…

I was talking to a co-developer last week during one of our lunch time walks(yes, we talk tech during out walks – even if our topic starts with something else, we always end up with tech stuff – once a geek, always a geek! :)). He is a C programmer and we often discuss Java vs C. One thing that came up last week was about Pointers. Having done both C and Java, I started explaining how Java…

There are five different implementation models of parameter passing. They are Pass-by-Value, Pass-by-Result, Pass-by-Value-Result, Pass-by-Reference, and Pass-by-Name. 

Pass-by-Value means that the value of the actual parameter is used to initialize the formal parameter. The formal parameter then acts as a local variable in the subprogram. This implements in-mode semantics.  

          Advantages: Is very fast for scalars (in linkage cost and access time)

          Disadvantages: if copies are used, additional storage required

Pass-by-Result is used for out-mode parameters. When Pass-by-Result is used, no value is transmitted to the subprogram. The corresponding formal parameter acts as a local variable, but before control is transferred back to the caller, its value is transmitted back to the caller’s actual parameter. This actual parameter must be variable.

          Advantages: Is very fast for scalars (in linkage cost and access time) 

          Disadvantages: there can be a parameter collision

Pass-by-Value-Result (or Pass-By-Copy) is used for inout-mode parameters when actual values are copied. It is a combination of pass-by-value and pass-by-result. The value of the actual parameter is used to initialize the formal parameter. The formal parameter then acts as a local variable.

         Advantages: same as Pass-by-Reference 

         Disadvantages: same as Pass-by-Reference 

Pass-by-Reference is another implementation model for inout-mode parameters. Instead of copying data values back and forth, it transmits an access path (usually an address) to the called subprogram.  This access path goes to the cell storing the actual parameter. The actual parameter is shared with the called subprogram.

         Advantages: the passing process is efficient

         Disadvantages: Access to formal parameters is slower, aliases can be created, accidental changes can be made to the actual parameter

Pass-by-Name is an inout-mode parameter transmission method. It does not correspond to a single implementation model. When using passing-by-name, the actual parameter is substituted for the formal parameter in all its occurrences in the subprogram.

        Advantages: none, kinda

        Disadvantages: A ton. Inefficient and super complex

There you go! Now you know everything you need to know about parameter-passing!