graph TD
    subgraph pay 方法
        P_A["开始 pay(amount)"] --> P_B{判断 amount > balance};
        P_B -- true --> P_C[抛出 InsufficientBalanceException “余额不足”];
        P_B -- false --> P_D[balance -= amount];
        P_D --> P_E[打印 “支付成功，当前余额: ” + balance];
        P_E --> P_F[结束 pay];
        P_C --> P_F;
    end

    subgraph main 方法
        M_A[开始 main] --> M_B[创建 TransCard 对象 card];
        M_B --> M_C[设置 card.balance = 100.0];
        M_C --> M_D{try 块};
        M_D --> M_E["调用 card.pay(50.0)"];
        M_E --> M_F["调用 card.pay(60.0)"];
                M_F --> M_G[结束 try 块];
        M_D -- InsufficientBalanceException --> M_H[捕获 InsufficientBalanceException];
        M_H --> M_I["打印异常信息 e.getMessage()"];
        M_I --> M_J[结束 main];
        M_G --> M_J;
    end