Просто так:
0{7,}|1{7,}
public static void main (String args[]) {
String zeros = "0000000";
String ones = "1111111";
String eights = "8888888";
String shuffle = "6516516";
System.out.println(zeros.matches("0{7,}|1{7,}")); // true
System.out.println(ones.matches("0{7,}|1{7,}")); // true
System.out.println(eights.matches("0{7,}|1{7,}")); // false
System.out.println(shuffle.matches("0{7,}|1{7,}")); // false
}