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I am working on an Android app, where I need to get a random object from firebase from a child? How to do it in java?
This is how I would do it, assuming I had a child with n objects:
If I didn't know how the value of n, I would first do this in my listener to get the total number of objects:
long n = dataSnapshot.getChildrenCount();
Then I would generate a random integer, i, between 0 and n. If you don't know how to do this, Google it.
Finally, I would get the ith item from the child:
final ArrayList<MyObject> objects = new ArrayList<>();
for (DataSnapshot child : children) {
MyObject object = child.getValue(MyObject.class);
objects.add(object);
}
MyObject objectToUse = objects.get(i);
"MyObject" should obviously be whatever class you're using.
Am I missing something? Is there a better way to do this? I'm pretty new to Android and very new to Firebase so take what I have to say with a big grain of salt haha.
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Say for instance I want to repeat the line of code
Integer int1 = new Integer(value1);
for many variables, such as int1 to int100. I am not asking about this exact task in particular - I am asking about any such situation where the code would be identical save for replacing small details like int1 and value1 with int2, value2. Is there a way to have the JVM complete this for me?
I am not even sure what approach to take on this or what term to search for more information. The only thing I can think to try is instead of typing "int1", having a loop that changes a string containing the name and attempting to pass the string as a symbol to the JVM but this of course does not work.
It was a little strange question and I don't know if I understood your meaning correctly or not.
But in this particular case, instead of repeating the code, you can use a data structure like an array. See Oracle tutorial.
int[] numvar = new int[arr.length];
for (int i = 0; i < args.length; i++) {
int someNumber = Integer.parseInt(args[i]);
numvar[i] = someNumber;
}
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I have store resource values in variables, and now I want to store this variable inside the Firebase database but the data type is Integer (int) and I don't know can we store an integer in Firebase or not.
I want to store below two variables of Integer type inside Firebase Database:
int textColor = ResourcesCompat.getColor(getResources(),R.color.black, null);
int textSize = (int) (getResources().getDimension(R.dimen.text10sp));
Can I store Int value inside Firebase database?
Sure you can, in a property of type Long, which is a supported data-type. An int value will always fit in a Long.
You can directly cast your int as Integer
Integer.valueOf(textColor)
Integer.valueOf(textSize)
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So lets say I want to randomly choose from the set of two numbers 1 and 3.
How do I go about doing that? Do I just assign int a to 1, int b to 3, and then do randomly select from a and b?
If there are only two numbers to choose from then you can use the value of a boolean, because it returns either true or false.
One-liner solution assuming that int a = 1 and int b = 3:
int randomOfTwoInts = new Random().nextBoolean() ? a : b;
If you have a specific list of numbers then put them in list structure (an array works well). Then you have the easier task of looking for a random index in the range from 0 to last array index. This post lists strategies for doing that:How do I generate random integers within a specific range in Java?
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How to judge whether a variable is an ArrayList in Java? Like the isInstance function.
Just use instanceof, blow is very simple example how to detect a variable is ArrayList:
List<String> strings = new ArrayList<>();
if (strings instanceof ArrayList) {
System.out.println("ArrayList");
}
a.getClass().getName() - will give you the type of the value of the variable, but not the variable's type.
boolean b = a instanceof String - will give you whether or not it is an instance of a specificclass.
I took this information from: How know a variable type in java?
This can happen. I'm trying to parse a String into an int and I'd like to know if my Integer.parseInt(s.substring(a, b) is kicking out an int or garbage before I try to sum it up.
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I create customer and computer arraylist from the existing cutomer and computer classes as belows
ArrayList<Customer> customer = new ArrayList<Customer>();
ArrayList<Computer> computer = new ArrayList<Computer>();
But I don't available to get option to retrieve the data. Can anyone solve this problem?
customer.get(i) i is the index.
computer.get(i)
You have get like this.
USE THIS METHOD AS SPECIFIED HERE. Read up on this stuff please!
http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html
get(int index)
Returns the element at the specified position in this list.
For Customer :
Customer ithCustomer = customer.get(i);(retrieve ith item in the customer list)