此java程序可以有三种用处：1、计算一次性投资本息和。2.计算periodically投资的本息和。3、计算loan（贷款）一定数目每月应还多少-This java program can use three types: 1, calculate principal and interest and a one-time investment. 2. Calculation of the principal and interest and investment periodically. 3, calculating the loan (loans) should be also a certain number of monthly number of