Simple calculator to evaluate arithmetic expressions
Thanks for sharing your code!

Pros


You actually created an instance of your class instead of using static methods
you have more than one method.


Cons

Naming

Finding good names is the hardest part in programming, so always take your time to think about the names of your identifiers.

Naming Conventions

Please read (and follow) the
Java Naming Conventions

E.g.: method names should be or start with a verb. Your method calculator() should better be named calculate().

Care for correct spelling

You named a variable problm. What is that? I suspect you misspelled problem, but it could something completely different. 

Declare variables as late as possible

Your method calculator() has two variables immediately declared at the beginning of the method. you first variable is result but it is the last one referenced. It is not needed untill the start of the for loop. Therefore it should be declared there.

The reason is that "late declaration" simplifies the use of your IDEs automated refactorings. One of them is extract method. 
You can use it to put the for loop into a separate method.
If you do it on your code as it is you would get this:

public void calculator() {
    double result=0;
    String problm = "";
    System.out.println("Use: \n\"/\" to divide \n\"x\" to multiply \n\"+\" for addition \n\"-\" to substract \n\n&gt;");

    problm = input.nextLine();

    result = calculateResult(problm, result);

    System.out.println("Answer is: " + result);
}

private double calculateResult(String problm, double result){
    for (int i=0; i&lt;problm.length();i++) {   
       // calculate the actual result...
    }
    return result;
}


You new method got an useless parameter.

If you had declared the variable result before the loop you could hav included it in the extracted patr and your code would be like this:

public void calculator() {
    System.out.println("Use: \n\"/\" to divide \n\"x\" to multiply \n\"+\" for addition \n\"-\" to substract \n\n&gt;");

    String problm = input.nextLine();

    double result = calculateResult(problm);

    System.out.println("Answer is: " + result);
}

private double calculateResult(String problm){
    double result=0;
    for (int i=0; i&lt;problm.length();i++) {   
       // calculate the actual result...
    }
    return result;
}