在我的计算机上运行代码但不在我的 friend 上运行代码时出现 java.lang.NullPointerException 错误

Question

您好，当尝试运行我的代码时，我不断收到 java.lang.NullPointerException 错误，但我确实知道它在 friend 计算机上工作不应该有任何错误。我正在使用Eclipse，似乎找不到问题。关于我做错了什么(也许是设置)的任何指示？谢谢

import java.util.List;
import java.util.Scanner;

public class Bank {

public static List< Account > accounts;
public static List< ICommand > commands;

public static void main( String[] args ) {
    commands.add( new CreateNewCommand() );
    commands.add( new OpenAccountCommand() );
    commands.add( new MakePaymentCommand() );
    commands.add( new IncrementMonthCommand() );

    Scanner input = new Scanner( System.in );

    boolean run = true;

    while ( run ) {
        System.out.println( "Commands:" );

        for ( ICommand command : commands ) {
            if ( command instanceof CreateNewCommand )
                System.out.println( ( ( CreateNewCommand )command ).command );

            if ( command instanceof OpenAccountCommand )
                System.out.println( ( ( OpenAccountCommand )command ).command );

            if ( command instanceof MakePaymentCommand )
                System.out.println( ( ( MakePaymentCommand )command ).command );

            if ( command instanceof IncrementMonthCommand )
                System.out.println( ( ( IncrementMonthCommand )command ).command );
        }

        // Close account is the same as open account, so no extra classes needed.
        System.out.println( "CloseAccount" );

        System.out.println();

        String line = input.nextLine();
        String[] inputArgs = line.split( "\\s+" );

        switch ( inputArgs[ 0 ] ) {
        case "CreateNew":
            CreateNewStruct structData0 = new CreateNewStruct();
            structData0.name = inputArgs[ 1 ];
            structData0.address = inputArgs[ 2 ];
            structData0.phone = inputArgs[ 3 ];
            structData0.ssn = inputArgs[ 4 ];
            structData0.age = inputArgs[ 5 ];
            structData0.initialBalance = Integer.parseInt( inputArgs[ 6 ] );
            structData0.loanLen = Integer.parseInt( inputArgs[ 7 ] );
            structData0.credit = Integer.parseInt( inputArgs[ 8 ] );

            structData0 = ( CreateNewStruct ) ( ( CreateNewCommand ) commands.get( 0 ) ).DoCommand( ( Object ) structData0 );
            accounts.add( structData0.account );
            System.out.println( "Account #" + structData0.account.acntNum + " was created." );
            break;

        case "OpenAccount":
            OpenAccountStruct structData1 = new OpenAccountStruct();
            structData1.acntNum = Integer.parseInt( inputArgs[ 1 ] );
            structData1.accounts = accounts;

            structData1 = ( OpenAccountStruct ) ( ( OpenAccountCommand ) commands.get( 1 ) ).DoCommand( ( Object ) structData1 );

            if ( structData1 == null ) {
                System.out.println( "Could not find account #" + Integer.parseInt( inputArgs[ 1 ] ) + "." );
                break;
            }

            Account account1 = structData1.account;

            System.out.println( "Account Number: " + account1.acntNum );
            System.out.println( "Name: " + account1.name );
            System.out.println( "Address: " + account1.address );
            System.out.println( "Phone: " + account1.phone );
            System.out.println( "SSN: " + account1.ssn );
            System.out.println( "Age: " + account1.age );
            System.out.println( "Initial Balance: " + account1.initialBalance );
            System.out.println( "Loan Length: " + account1.loanLen );
            System.out.println( "Credit: " + account1.credit );
            System.out.println( "Monthly Payment: " + account1.monthlyPayment );
            System.out.println( "Interest Rate: " + account1.interestRate );
            System.out.println( "Balance: " + account1.balance );

            break;

        case "MakePayment":
            MakePaymentStruct structData2 = new MakePaymentStruct();
            structData2.acntNum = Integer.parseInt( inputArgs[ 1 ] );
            structData2.payment = Double.parseDouble( inputArgs[ 2 ] );
            structData2.accounts = accounts;

            structData2 = ( MakePaymentStruct ) ( ( MakePaymentCommand ) commands.get( 2 ) ).DoCommand( ( Object ) structData2 );

            if ( structData2 == null ) {
                System.out.println( "Could not find account #" + Integer.parseInt( inputArgs[ 1 ] ) + "." );
                break;
            }

            Account account2 = structData2.account;

            System.out.println( "New balance for account #" + account2.acntNum + " is " + account2.balance );

            break;

        case "IncrementMonth":
            IncrementMonthStruct structData3 = new IncrementMonthStruct();
            structData3.acntNum = Integer.parseInt( inputArgs[ 1 ] );
            structData3.accounts = accounts;

            structData3 = ( IncrementMonthStruct ) ( ( IncrementMonthCommand ) commands.get( 3 ) ).DoCommand( ( Object ) structData3 );

            if ( structData3 == null ) {
                System.out.println( "Could not find account #" + Integer.parseInt( inputArgs[ 1 ] ) + "." );
                break;
            }

            Account account3 = structData3.account;

            System.out.println( "Added the monthly interest for account #" + account3.acntNum );

            break;

        case "CloseAccount":
            OpenAccountStruct structData4 = new OpenAccountStruct();
            structData4.acntNum = Integer.parseInt( inputArgs[ 1 ] );
            structData4.accounts = accounts;

            structData4 = ( OpenAccountStruct ) ( ( OpenAccountCommand ) commands.get( 1 ) ).DoCommand( ( Object ) structData4 );

            if ( structData4 == null ) {
                System.out.println( "Could not find account #" + Integer.parseInt( inputArgs[ 1 ] ) + "." );
                break;
            }

            Account account4 = structData4.account;

            if ( account4.balance > 0.00d ) {
                System.out.println( "There is still money that needs to be payed!" );
                break;
            }

            accounts.remove( account4 );

            break;

        default:
            run = false;
            break;
        }

        System.out.println();
    }

    input.close();
}

}

Answer 1

您在哪里定义命令列表？你有一个声明，但据我所知，你并没有创造任何东西。

public static List< ICommand > commands;


commands = new List< .... ?

我可以看到您定义了命令本身，但没有定义列表。