When the amount of intensive reading to be processed is too large to be processed by double type, two APIs, BigInteger and BigDecimal, can be called for processing. Among them, BigInteger supports integers with arbitrary precision, and BigDecimal supports fixed points with arbitrary precision.
ArrayList inherits from AbstractList and implements the List interface. The bottom layer realizes the dynamic change of capacity based on array. Allow the existence of null. It is an array queue, which provides related functions such as adding, deleting, modifying and traversing. In a topic, if the number or type of objects is not known in advance, it cannot be represented by an array.