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Thread: Java application for infinite series that calculates pi

  1. #1
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    Default Java application for infinite series that calculates pi

    Hi

    I am having trouble compiling my code for a java application that is supposed to print out the infinite series for Pi. Here is my java code:

    //a java application that generates the infinite series for Pi, ie 3.14159...=4-4/3+4/5-4/7+4/9
     
    public class Pi{
     
    	public static void main(String args[]){
     
    //declare and initialize variables
     
    long counter=1;
    double pi;
     
     
    double total=0;
     
    for(counter=1; counter<=1000; counter++)
     
    pi=4+4*(Math.pow(-1,counter))/(2*counter+1);
     
     
     
    total=total+pi;
     
    System.out.printf("Infinite series for Pi is %f", total);
     
    }//end main
     
    }//end class

    Here is the error in my output that results when I attempt to compile my code:

    C:\Users\anonymous\Desktop\chapter five exercises for java\Pi.java:21: error: variable pi might not have been initialized
    total=total+pi;
    ^
    1 error

    Tool completed with exit code 1
    Why do I need to initialized pi when I already initialized the total?


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    Member Ada Lovelace's Avatar
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    Default Re: Java application for infinite series that calculates pi

    Because double is a primitive type - and is assigned null by default.
    Therefore - when you attempt to use the variable in the assignment statement,
    the compiler does not know what pi was initialized to before the statement.
    Assign pi a base value.

    Wishes Ada xx
    If to Err is human - then programmers are most human of us all.
    "The Analytical Engine offers a new, a vast, and a powerful language . . .
    for the purposes of mankind
    ."
    Augusta Ada Byron, Lady Lovelace (1851)

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    Administrator copeg's Avatar
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    Default Re: Java application for infinite series that calculates pi

    Because double is a primitive type - and is assigned null by default.
    Not sure I understand (or agree with) this statement.

    The compiler complains because it requires variables to be initialized by default. It is called Definite Assignment, outlined in more detail in the JRE Spec

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    Default Re: Java application for infinite series that calculates pi

    Nevermind , problem solved

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    Default Re: Java application for infinite series that calculates pi

    I also don't agree. class level variables don't need to be initialized. Variables in a method must be initialized.
    double is a primitive and when defined at the class level is given a default value of 0.0
    For example. Some code from the middle of my test program:
    class TestCode18 {
       double xxxx;
       public TestCode18() {
                System.out.println("xxxx="+xxxx);  // xxxx=0.0
       }
     
       public static void main(String[] theArgs) throws Exception {
          new TestCode18();
       }
    }
    If you don't understand my answer, don't ignore it, ask a question.

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    Default

    You should always initialise variables with a value. If they're not given a value, they get assigned null.

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    Default Re: Java application for infinite series that calculates pi

    Quote Originally Posted by CDeighan View Post
    You should always initialise variables with a value. If they're not given a value, they get assigned null.
    This is not true for primitives, and only true for class variables. See Norm's answer.

    And, actually, you should /not/ always explicitly assigned class variables, primitives or objects. Many compilers actually do (or did -- you'd have to look at the bytecode) not optimize the unneeded assigment to 0 or null away. That is, they emit larger code for the class.

    Of course, in this case, the class variable does need to be assigned to some default prior to be used on the right-hand side of an assignment, because the compiler can't be sure it was assigned something in the loop.

    In many cases lke this I will show the assignment to a default directly above the condition that will probably change it, so the state of the property is determined in the same chunk of code.

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    Member Ada Lovelace's Avatar
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    Default Re: Java application for infinite series that calculates pi

    Interesting topic - and thank you everyone for their insights. Can I apologise for
    my mistake in my previous answer, I think I got class-type and primitive's a bit
    muddled

    On this note - to prevent such an error, would it be feasible to, instead of doing this:

    double x;

    Do this:

    double x = input.nextDouble()

    Would this prevent such a problem in such a trivial case? The actual
    assignment is being done as at declaration time (think this was mentioned
    above) - just a query that's all.

    Wishes Ada xx
    If to Err is human - then programmers are most human of us all.
    "The Analytical Engine offers a new, a vast, and a powerful language . . .
    for the purposes of mankind
    ."
    Augusta Ada Byron, Lady Lovelace (1851)

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    Default Re: Java application for infinite series that calculates pi

    In general, the only reason to have declared but uninitialized class variables is if they are also class properties. In which case there will, or should, be setters, getters and or initializers in constructors.

    Otherwise, declare and, if necessary, initialize them as needed. This isn't C, so don't bother with declaring plain old variables up front. Of course, when doing toy apps like this, with everything in main(), the line between class variables, locals and properties is blurred. Java, unlike C#, doesn't actually enforce this distinction, so it is up to the person between the keyboard and the chair to understand what they are doing.

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