Cant we give object names dynamically

[somashaker goud]

I am trying to create biginteger object dynamically but its throwing me an error.

        for(int unsorted_i=0; unsorted_i < n; unsorted_i++){
            String val = in.next();
            unsorted[unsorted_i] = val;
            //String obj ="big"+""+unsorted_i ;
            BigInteger "obj"+""+unsorted_i  = new BigInteger(val);
            bigInt[unsorted_i] = "obj"+""+unsorted_i;
        }

below is the error which I am getting.

Solution.java:19: error: not a statement
            BigInteger "obj"+""+unsorted_i  = new BigInteger(val);
            ^
Solution.java:19: error: ';' expected
            BigInteger "obj"+""+unsorted_i  = new BigInteger(val);
                      ^
2 errors

[Bear Bibeault]

No, you can't create variable names dynamically. If you want to associate values with run-time names, look into a Map implementation.

[Jesper de Jong]

Objects do not have names. Variables have names. A variable is not an object; it's important to understand the difference between variables and objects. A variable (of a non-primitive type) is a reference to an object. You can have multiple variables that refer to the same object.

Also, you have to understand the difference between compile time and runtime.

Compile time is when the compiler translates your source code to an executable class file.

Runtime is when you run the compiled program. Runtime is always after compile time - you first have to compile a program before you can run it.

Many concepts in Java programming, including names of variables, have to be known at compile time. What you are trying to do in the code you posted is create a variable name at runtime. That is not possible, because the variable name has to be known at compile time, which is before runtime.

If you want to create and store objects dynamically, you'll have to store them in a collection such as a List, Map or Set. Have a look at the Collections tutorial from Oracle to learn about collections.

[fred rosenberger]

i always figure variable names are for programmers who are reading code.  What possible advantage is there to creating a variable name at runtime, when the programmer can't see it?

[Ryan McGuire]

fred rosenberger wrote:i always figure variable names are for programmers who are reading code.  What possible advantage is there to creating a variable name at runtime, when the programmer can't see it?

The advantage of dynamically-generated variable names would be exactly the same advantages that Map implementations already have.  You don't need to know the "key" to get a given value at programming/compile time, but it will be known at run time.

[Yosuf Ibrahim]

fred rosenberger wrote:i always figure variable names are for programmers who are reading code.  What possible advantage is there to creating a variable name at runtime, when the programmer can't see it?

Do you know you can create an ArrayList that can hold references to objects dynamically?

[Henry Wong]

Yosuf Ibrahim wrote:
Do you know you can create an ArrayList that can hold references to objects dynamically?

Yes, but the question was about assigning names to it dynamically. An ArrayList doesn't allow a name, or anything (but an index) to be attached dynamically. This is why, Bear recommended using a Map, and not a List, in his above post.

Henry

[Ryan McGuire]

Back to the original post...

There are three levels of improvement you could make to the code:
1. Implement Bear's suggestion by using a Map of some kind.

        Hashtable tempBigInts<String, BigInteger> = new Hashtable<String, BigInteger>();
        for(int unsorted_i=0; unsorted_i < n; unsorted_i++) {
            String val = in.next();
            unsorted[unsorted_i] = val;
            tempBigInts.put("obj" + unsorted_i, new BigInteger(val));
            bigInt[unsorted_i] = tempBigInts.get("obj" + unsorted_i);
        }

2. You should then notice that the temporary BigInteger values aren't being used outside the for() loop and only one is being used each time through the loop.  Therefore, you don't need to have a different BigInteger variable for each value you read in.  Just reuse the same name each time through the loop:

        for(int unsorted_i=0; unsorted_i < n; unsorted_i++) {
            String val = in.next();
            unsorted[unsorted_i] = val;
            BigInteger tempBigInt  = new BigInteger(val);
            bigInt[unsorted_i] = tempBigInt;
        }

3. Even better... just assign the new BigInteger to the bigInt array element without using the temporary variable.

        for(int unsorted_i=0; unsorted_i < n; unsorted_i++) {
            String val = in.next();
            unsorted[unsorted_i] = val;
            bigInt[unsorted_i]  = new BigInteger(val);
        }