java程序要产生日期型的随机函数应该怎么写呢？

import java.util.*;
import java.util.Random;

public class RandomDate
{
public static void main(String args[])
{
int data=0,data2=0,count=1,count2=1;
boolean flag = true,flag2=true;
Random random1=new Random();
Random random2=new Random();

ArrayList al1=new ArrayList();
ArrayList al2=new ArrayList();
do
{

int num=random1.nextInt(12)+1;
int num2=random2.nextInt(31)+1;

String str1=String.valueOf(num);
String str2=String.valueOf(num2);
//月
for(int i=0;i<al1.size();i++)
{
String s=(String)al1.get(i);
int a=Integer.parseInt(s);
if(a==num)
{
data++;
}
}
if(data==0)
{
al1.add(str1);
//System.out.println(num);
count++;
}
data = 0;
if(count>12)
{
flag = false;
}

//日
for(int j=0