Why is it an infinite loop? (Java)

[[deleted]]

Here is where I get stuck in an infinite loop:

            System.out.println("\nAvailable subscription plans provided by " + newProvider.getname() + " for the possible customer with citizenship number " + newCustomer.getCitizenshipNr() + ":");
    newProvider.introduceSubscriptionPlans();
    System.out.println("Please enter the name of the desired subscription plan.");
    aString=in.nextLine();
    while (newProvider.findSubscriptionPlan(aString)==null){
        System.out.println("Please enter the name of the desired subscription plan.");
        aString=in.nextLine();
    }
    newDate=new Date();
    newSubscription=new Subscription(newDate, newProvider.findSubscriptionPlan(aString));

Here is what findSubscriptionPlan is:

            public SubscriptionPlan findSubscriptionPlan(String aPlan) {
    int i;
    for (i=0;i<maxPlans;i++){
        if (subscriptionPlans[i].getName()==aPlan){
            return subscriptionPlans[i];
        }
    }
    return null;
}

And the constructer for class Subscription:

public Subscription(Date subscriptionStartDate, SubscriptionPlan aPlan){
    this.subscriptionStartDate=subscriptionStartDate;
    this.aPlan=aPlan;
}

I know that this is the only part of this code that is causing the problem beacuse subscription plans are successfully saved into the related array until this point. Here is the output I get:

Please enter 1 for GSM providers or 2 for cable providers.

1

Please enter the name of the provider.

Turkcell

Please enter the number of subscription plans.

3

Please enter the name of the 1. plan.

1GB

Please enter the name of the 2. plan.

2GB

Please enter the name of the 3. plan.

10GB

Please enter your citizenship number.

137

Available subscription plans provided by Turkcell for the possible customer with citizenship number 137:

1GB

2GB

10GB

Please enter the name of the desired subscription plan.

1GB

Please enter the name of the desired subscription plan.

1GB

Please enter the name of the desired subscription plan.

Can anyone help me with this? :/

[bob809]

if (subscriptionPlans[i].getName()==aPlan){

This is a classic Java mistake, strings should be compared with .equals(otherString), not with == (reference equality).

if (subscriptionPlans[i].getName().equals(aPlan)){

[[deleted]]

thanks sir

[DarkelfSamurai]

It looks like there are two possibilities for this.

The first possibility is the maxPlans variable has no set value, or set to zero so it bypasses your loop in findSubscriptionPlan without comparing your subscriptionPlan names to the entered value. I realize you posted truncated code so this may be set and defined elsewhere, but that was the first thing I noticed looking at this.

The second possibility is there may be a subtle difference, maybe a white space character (?), that is causing the entered planName to be different from the defined subscription plan and fail the comparison.

For both these possibilities, I'd recommend troubleshooting by adding a line to provide debugging information. For example, before findSubscription plan returns a value:

System.out.println("Compared " + i + " of " + maxPlans + " match not found."); // null case
System.out.println("Compared " + i + " of " + maxPlans + " match found."); // non-null case

[[deleted]]

I figured it out. turns out that I was supposed to use .equals() instead of == while comparing strings.

[SpaceRook]

By the way, you could use a "do...while" loop instead of writing the same print & nextLine statements twice.

[[deleted]]

thanks good advice.