Проверка последовательных дат Java

var arr = ["2017-06-17", "2017-06-18", "2017-06-19", "2017-06-18"]; 
var arr2 = ["2017-06-17", "2017-06-18", "2017-06-19", "2017-06-20"]; 
var arr3 = ["2017-12-30", "2017-12-31", "2018-01-01", "2018-01-02"]; 
var arr4 = ["2017-12-30", "2017-11-31", "2017-12-30", "2018-01-02"]; 
 
 
function isDateSequence(arr) { 
  var d1, d2 = ""; 
   
  for (var i = 0; i < arr.length - 1  ; ++i) { 
      d1 = new Date(arr[i]); 
      d2 = new Date(arr[i + 1]);    
             
      // 86400000 - это +1 день 
      if (d1.getTime() + 86400000 != d2.getTime())  {         
        return false; 
      } 
  } 
   
  return true; 
}   
 
console.log(isDateSequence(arr)); 
console.log("---------------"); 
console.log(isDateSequence(arr2)); 
console.log("---------------"); 
console.log(isDateSequence(arr3)); 
console.log("---------------"); 
console.log(isDateSequence(arr4));