java得到指定位数随机密码（由数字，区分大小写的字母组成）

/**
*获取指定位数密码
*/
public String getCode(int length){
char[] m = new char[length];
for(int i = 0;i < length;i++){
m[i] = get();
}
return new String(m);
}

private char get(){
int begin = 0;
int end = 0;
switch(new Random().nextInt(3)){
case 0:
begin = 10;
end = 48;
break;
case 1:
begin = 26;
end = 65;
break;
case 2:
begin = 26;
end = 97;
break;
}
return (char) (new Random().nextInt(begin) + end);
}