how to random questions in android

i'm developing a simple quiz in my android project, and i create 15 sample question. i want to random that questions, but i don't know how to write the code. help me please!! and thanks for your time. Here is my code

package com.adm.kana;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;

public class Kuis_Hiragana extends Activity implements View.OnClickListener {
TextView pertanyaan, salahbenar;
Button jawab, lanjut;
EditText jawaban;
int benar=0, salah=0, index=0;
String[] soal={"ぐ ","く ","あ ","ば ","き ゅ ","ち ょ ","ち ","お ","ぽ ","ね ","わ ","む ","れ ","ぞ ","し ょ "};
String[] jawabann={"gu","ku","a","ba","kyu","cho","chi","o","po","ne","wa","mu","re","zo","sho"};

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.kuis);

    salahbenar=(TextView)findViewById(R.id.salahbenar); salahbenar.setText("");
    pertanyaan=(TextView)findViewById(R.id.soal); pertanyaan.setText(soal[0]);
    lanjut=(Button)findViewById(R.id.lanjut_soal); lanjut.setOnClickListener(this);
    jawab=(Button)findViewById(R.id.btn_jawab); jawab.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    salahbenar=(TextView)findViewById(R.id.salahbenar);
    jawaban=(EditText)findViewById(R.id.jawab);
    if (v==jawab){
        String jawab1=jawaban.getText().toString();
        if (jawab1.equalsIgnoreCase(jawabann[index]))
        { salahbenar.setText("BENAR"); benar++; }
        else
        { salahbenar.setText("SALAH"); salah++;}
    }
    else if (v==lanjut){
        if (index<soal.length-1){
            index++;
            pertanyaan.setText(soal[index]);
            jawab.setEnabled(true);
            lanjut.setVisibility(View.VISIBLE);
            jawaban.setText("");
            salahbenar.setText("");
        }
        else {
            Intent i = new Intent(Kuis_Hiragana.this, Hasil.class);
            i.putExtra("BENAR", benar);
            i.putExtra("SALAH", salah);
            startActivity(i);
            onStop(); System.exit(0);
        }
    }
}

}