just one Edit instead of two ( AlertDialog )

Question 1

the second view it s overriding the first in AlertDialog you put only one view! so use a linearlayout trick as here below:

String s;

public void btn_own(View view) {
    int a, b, c;        // a : untere Grenze , b : obere Grenze


AlertDialog.Builder alert = new AlertDialog.Builder(this);

    alert.setTitle("Enter range");
     LinearLayout linearLayout = new LinearLayout(context);
     linearLayout.setOrientation(1);
     linearLayout.setGravity(Gravity.CENTER);


    final EditText inputa = new EditText(this);
    final EditText inputb = new EditText(this);
     linearLayout.addView(inputa );
     linearLayout.addView(inputb );

    alert.setView(linearLayout );


        alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int whichButton) {

                int aa = 0;
                int bb = 0;
                int cc = 0;
                int e = 0;
                try {
                    aa = Integer.parseInt(inputa.getText().toString());
                }   catch (NumberFormatException f) {
                    System.out.println("not a number: " + inputa.getText().toString());
                    f.printStackTrace();
                }

                try {
                    bb = Integer.parseInt(inputb.getText().toString());
                }   catch (NumberFormatException g) {
                    System.out.println("not a number: " + inputb.getText().toString());
                    g.printStackTrace();
                }
                cc = bb - aa;
                Random rand = new Random();
                int d = rand.nextInt(cc);
                e = d + bb;
                Integer out = new Integer(e);
                s = out.toString();

                new AlertDialog.Builder(Decider.this)
                        .setMessage(s)
                        .show();

            }
        });
    alert.show();

}

Question 2

by "one edit", I assume you mean "one edittext". the reason why you are getting only one edittext is that you are using setView() method twice with two different edittext components. setView() method is actually used to set the view of the dialog, so the solution to your problem is that you can use a layout file with two edittext's wrapped inside a linearlayout. here is how you can do this -

define a layout file in your layout folder like below and give a name to this layout file of your choice

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/set_default_header"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:background="@drawable/lem_background_small"
     android:orientation="vertical"
     android:padding="10dp" >
     <EditText
        android:id="@+id/randomno1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="8dp"
        android:layout_gravity="bottom"
        android:inputType="text"
        android:text=""
        android:hint="Enter Budget"
        android:textAppearance="?android:attr/textAppearanceSmall" />
     <EditText
        android:id="@+id/randomno2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"
        android:layout_gravity="bottom"
        android:inputType="text"
        android:text=""
        android:hint="Enter Budget"
        android:textAppearance="?android:attr/textAppearanceSmall" />
      </LinearLayout>

the in the setView() method write setView(R.layout.yourlayoutfilename) instead of

    alert.setView(inputa);
    alert.setView(inputb);

and then inside setPositiveButton() method of your dialog you can access these edittexts by their id and do what you want to.

I hope this solves your problem.