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public class PostActivity extends AppCompatActivity{

    private Button buttonPrefecture;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.post_activity);

        buttonPrefecture = (Button)findViewById(R.id.button_prefecture);

        buttonPrefecture.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                choosePrefecture();
            }
        });
    }

    public void choosePrefecture(){
        final String[] items = {"item_0", "item_1", "item_2"};
        int defaultItem = 0; // デフォルトでチェックされているアイテム
        new AlertDialog.Builder((this))
                .setTitle("Selector")
                .setSingleChoiceItems(items, defaultItem, null)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // item_which selected
                    }
                })
                .setNegativeButton("Cancel", null)
                .show();
    }
}