确定2个错误：
1） 你在测试吗 userPIN != savedPIN 但是你接受这个值变成变量 pass 你什么都不做。
2） 移除第一个循环中的中断，它将始终不循环地退出。
它应该看起来像：

while(pass!= savedPIN)  
    {
     System.out.print("Please enter your correct PIN : ");
     Scanner again = new Scanner(System.in);
     int pass = again.nextInt();
    }

删除“break；”语句并使用新的pin更新userpin，如下所示：

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        int savedPIN = 4444;
        Scanner input = new Scanner(System.in);
        System.out.println("Enter password");
        int userPIN = input.nextInt();
        double withdraw = 0.0, amount = 0.0, deposit = 0.0;

        while (userPIN != savedPIN) {
            System.out.print("Please enter your correct PIN : ");
            Scanner again = new Scanner(System.in);
            userPIN = again.nextInt();
        }

        while (userPIN == savedPIN) {

            System.out.println(" 1 - Inquire Balance \n 2 - Withdraw \n 3 - Deposit \n 0 - Quit ");

            Scanner inputNum = new Scanner(System.in);
            int number = inputNum.nextInt();
            switch (number) {
                case 1:
                    System.out.println("The current balance is $" + amount);
                    break;

                case 2:
                    System.out.println("Enter the amount to withdraw : ");
                    withdraw = input.nextDouble();
                    if (amount >= withdraw) {
                        amount = amount - withdraw;
                        System.out.println("The current balance is $" + amount);
                    } else {
                        System.out.println("Insufficient balance");
                    }
                    break;

                case 3:
                    System.out.println("Enter the amount to deposit : ");
                    deposit = input.nextDouble();
                    amount = amount + deposit;
                    System.out.println("The current balance is $" + amount);
                    break;

                case 0:
                    System.exit(4);
            }

        }

    }
}