Populate a string-array without having to enter every entry

Question

I am creating a spinner in my current layout file, and the contents of this spinner range from 1.0 mA, all the way to 100.0mA. Each increment increases by 0.1 mA. Is there a way to have some sort of loop to populate this string-array, other than manually entering each entry in my string-array file?

Answer 1

You can use BigDecimal to do this. Here's an example that prints them to the screen from 1.0 to 3.0. You can adapt as necessary.

By using BigDecimal, you will not have rounding errors internally or externally, meaning if you extend it to a bigger number down the road, you won't run into those issues. Big Decimal was designed for this kind of thing.

import java.util.*;
import java.math.*;
class Amps {
    public static void main(String[] args) {
        List<String> strs = new ArrayList<String>();
        BigDecimal max = new BigDecimal("3.0");
        BigDecimal inc = new BigDecimal("0.1");
        for(BigDecimal cur = new BigDecimal("1.0"); cur.compareTo(max) <= 0; cur = cur.add(inc)) {
            strs.add(cur.toString() + "mA");
        }
        System.out.println(strs);
    }

}

If you're wondering about the speed, using the BigDecimal is actually faster than using the formatter. Here's a small test that runs them back and forth for a sample size of about 1,000,000 strings:

import java.math.*;
import java.text.*;
import java.util.*;
class Amps {
    public static void main(String[] args) {
        usingBig();
        usingPrim();
        usingBig();
        usingPrim();
        usingBig();
        usingPrim();
        usingBig();
        usingPrim();
        usingBig();
        usingPrim();
    }

    static void usingBig() {
        long then = System.currentTimeMillis();
        List<String> strs = new ArrayList<String>(1000000);
        BigDecimal max = new BigDecimal("100000.0");
        BigDecimal inc = new BigDecimal("0.1");
        for(BigDecimal cur = new BigDecimal("1.0"); cur.compareTo(max) <= 0; cur = cur.add(inc)) {
            strs.add(cur.toString() + "mA");
        }
        long now = System.currentTimeMillis();
        System.out.println("Big: " + (now - then));
    }

    static void usingPrim() {
        long then = System.currentTimeMillis();
        DecimalFormat formatter = new DecimalFormat("0.0");
        List<String> strs = new ArrayList<String>(1000000);
        float max = 100000.0f;
        float inc = 0.1f;
        for(float cur = 1.0f; cur <= max; cur += inc) {
            strs.add(formatter.format(cur) + "mA");
        }
        long now = System.currentTimeMillis();
        System.out.println("Prim: " + (now - then));
    }

}

With a result of:

C:\files\j>java Amps
Big: 1344
Prim: 5172
Big: 1047
Prim: 4656
Big: 1172
Prim: 4531
Big: 1125
Prim: 4453
Big: 1141
Prim: 4547

Even without the DecimalFormatter, primitives are still slower than BigDecimal. See below the results of if I comment out the DecimalFormatter and it's format call (using instead cur + "mA" to add to the list).

C:\files\j>java Amps
Big: 1328
Prim: 1469
Big: 1093
Prim: 1438
Big: 1375
Prim: 1562
Big: 1204
Prim: 1500
Big: 1109
Prim: 1469

Answer 2

Create a SpinnerAdapter and hook it up to your spinner. Then you can loop through calling adapter.add(item1), adapter.add(item2), etc...

Check this out also: How can I add items to a spinner in Android?

For example,

Spinner spinner = (Spinner) findViewById(R.id.spinner);

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, YOUR_STRING_ARRAY);

adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

spinner.setAdapter(adapter);

Answer 3

Of course you can:

String[] data = new String[991];

int i = 0;
for(float f=1.0f; f<=100.0f; f+=0.1f) {
    data[i++] = "" + f + "A";
}

EDIT: If you want to put this array in your XML file, you can use any programming language you want to generate this array as a one-off. For example, this java code will do the grunt work for you:

import java.text.*;
public class T {
  public static void main(String[] args) {
  DecimalFormat formatter = new DecimalFormat("0.0");

    for(float f=1.0f; f<=100.0f; f+=0.1f) {
      System.out.println("\"" + formatter.format(f) + "A\",");
    }
  }
}

Compile/run it: javac T.java followed by java T > output.txt. Now open the output.txt file in a text editor and copy/paste your array.

Answer 4

List<String> list = new ArrayList<String>();

now using for loop you can add data in list and set list to spinner..

for(float value=1.0f;value<100.0f;){
        String str = String.valueOf(value);
        list.add(value+"mA");
          value+=0.1f;       
}

Answer 5

Try a loop that generates strings

List<String> list = new ArrayList<String>();
int endCount = (100. - 1.0) / .1
For(int i = 0; i < endCount; i++){

    String stringToAdd = String.format("%.1f mA", 1.0 + ((float)i * 0.1));

    // Add stringToAdd to your array
    list.add(stringToAdd);
}

Answer 6

You will have to implement a SpinnerAdapter class, similar to this one:

public class MySpinnerAdapter implements SpinnerAdapter {
   private List<String> steps = new ArrayList<String>();
   public MySpinnerAdapter(double min,double max,double increment) {
      for(double f=min;f < max;f+=increment) steps.add(String.valueOf(f)+" mA");
   }
   public int getCount() {
      return steps.size();
   }
   public View getView(int position, View convertView, ViewGroup parent) {
      TextView t = new TextView(YourActivity.this);
      t.setText(steps.get(position));
      return t;
   }
   public boolean isEmpty() {
      return (steps.size() == 0);
   }
   public View getDropDownView(int position, View convertView,ViewGroup paret) {
      if(convertView != null) return(convertView);
      return(getView(position,convertView,parent));
   }
   public Object getItem(int position) {
      return(steps.get(position));
   }
   public long getItemId(int position) {
      return position;
   }
   public int getItemViewType(int position) {
      return 0;
   }
   public int getViewTypeCount() {
      return 1;
   }
   public boolean hasStableIds() {
      return true;
   }
   public void registerDataSetObserver(DataSetObserver observer) {
   }
   public void unregisterDataSetObserver(DataSetObserver observer) {
   }
}

Then you have to set a new instance of this class into your Spinner:

Spinner s = (Spinner) findViewById(R.id.YourSpinnerId);
s.setAdapter(new MySpinnerAdapter(1.0,100.0,0.1));