import java.util.Scanner;

public class Account {
 static double rate = 0.0265;
 
 public void calculateInterest(int principal, int years) {
  double var= 1;
  for (int i = 1; i <= years; i++) {
   var = var*(1 + rate);
  }
  double interests = principal * var - principal;
  System.out.println(years + "年后，存入" + principal + "元所获利息为" +  interests + "元RMB。");
 }

 public void changeRate(double newrate) {
  rate = newrate/100;
 }
 
 public static void main(String[] args) {
  int principal;
  int years;
  Scanner sc = new Scanner(System.in);
  System.out.println("当前银行死期年利率为" + (rate * 100) + "%。\n请输入存款本金：");
  principal = sc.nextInt();
  System.out.println("请输入存款年限：");
  years = sc.nextInt();
  Account oldAccount = new Account();
  oldAccount.calculateInterest(principal, years);
  System.out.println("利率变了！请输入调整后的存款利率（利率格式:2.65）：");
  double changedrate = sc.nextDouble();
  Account newAccount = new Account();
  newAccount.changeRate(changedrate);
  System.out.println("请输入存款本金：");
  principal = sc.nextInt();
  System.out.println("请输入存款年限：");
  years = sc.nextInt();
  newAccount.calculateInterest(principal, years);
  sc.close();
 }
}

1、for循环的作用就是计算年利率的吧。利息=本金*利率*年限的这样不就可以算出利息么

2、String.format("%.3f", interests)   String format这个代码一直不太懂是什么作用呢！