遇到Missing Return Value怎么解决？java报错

遇到Missing Return Value怎么解决？java报错

在编写java的样例代码时出现这种问题。这种情况应该如何解决和避免那？

public class SavingsAcc2 {
    private double balance;
    private double interest;
    public SavingsAcc2() {
        balance = 0.0;
        interest = 6.17;
    }
    public SavingsAcc2(double initBalance, double interested) {
        balance = initBalance;
        interest = interested;
    }
    public SavingsAcc2 deposit(double amount) {
        balance = balance + amount;
        return;
    }
    public SavingsAcc2 withdraw(double amount) {
        balance = balance - amount;
        return;
    }
    public SavingsAcc2 addInterest(double interest) {
        balance = balance * (interest / 100) + balance;
        return;
    }
    public double getBalance() {
        return balance;
    }
}

原因是什么，为什么会发生异常，以及下面到底发生了什么。如果有人能帮忙？提前谢谢