ArrayList不存储值

Question

I am new to the concept of ArrayLists. I am using them as I want a dynamic array that isn't limited in the size of how many values it can hold in sequence. But the method I am using is not storing values correctly. I only keeps one value being the value 1. My code is as follows:

public void Rand(){
Random rand = new Random();
int Val = rand.nextInt(5); 
ArrayList<Integer> ValList = new ArrayList<Integer>();
ValList.add(Val);
Log.d("LOOK", Integer.toString(ValList));   
Log.i("VALUE LIST ", ValList.size()+" <<<<LIST HERE"); }

This process is called in oncreate and then returned to on a loop Ideally every time this class runs a new random number will be added to the array in sequence.

This is the relevant info on the logcat:

03-05 19:15:15.020: D/LOOK(21325): 3
03-05 19:15:15.020: I/VALUE LIST(20883): 1 <<<<LIST HERE
03-05 19:15:15.040: D/LOOK(21325): 5
03-05 19:15:15.040: I/VALUE LIST(20883): 1 <<<<LIST HERE

As you can see it only stores the value 1 even though the random value is not 1. Am I using the wrong type of array or implementing it incorrectly?

The output i'd want to see is something like this:

03-05 19:15:15.020: D/LOOK(21325): 3
03-05 19:15:15.020: I/VALUE LIST(20883): 3 <<<<LIST HERE
03-05 19:15:15.040: D/LOOK(21325): 5
03-05 19:15:15.040: I/VALUE LIST(20883): 3, 5 <<<<LIST HERE

Answer 1

Because, Your ArrayList<Integer> ValList = new ArrayList<Integer>(); has local scope for Rand() method only, So its has new instance every time you called Rand() function.

Just declare ArrayList<Integer> ValList = new ArrayList<Integer>(); as class level scope.

And use,

Like,

// Class level member declaration
ArrayList<Integer> ValList = new ArrayList<Integer>();

public void Rand(){
          Random rand = new Random();
          int Val = rand.nextInt(5); 

          ValList.add(Val);
          Log.d("LOOK", ValList.toString()); 
          // Also here you are printing size of Arraylist not a content of arraylest
          Log.i("VALUE LIST ", ValList.size()+" <<<<LIST HERE"); 
 }

To print specific object value you have to get object from ArrayList using .get() with position of object, or use .toString() to print all list contents

Log.i("VALUE LIST ", ValList.toString()+" <<<<LIST items"); // using .toString() to print all contents of List

Update:

As I have doubt over this line throws Exception (But from your logcat its working fine, as list contains only one item)

Log.d("LOOK", Integer.toString(ValList)); 

As you are trying to print values of list valList , simply use .toString() like, ValList.toString()

Answer 2

You are trying to print size of your list.

Log.i("VALUE LIST ", ValList.size()+" <<<<LIST HERE"); } Log.i("VALUE LIST ", ValList.size()+" <<<<LIST HERE"); } // wrong (as per ques)

If you want to know what your array contains, try to print the content of your array.