Java - If语句逻辑错误

Question

事件的顺序应该是:

1) I enter two.
2) I am prompted to choose a name.
3) I choose either Washington/ Franklin/ Hamilton.
4) I'm asked which denomination does this name appear on.
5) I give the answer.

但是，当我进入华盛顿参加第三部分时 - 我被告知这是一个无效号码。我不明白为什么会这样。

public static void main(String[] args) {
    // TODO code application logic here
    System.out.println("Type 1 to enter a denomination, 2 to enter a last name");
    Scanner in = new Scanner(System.in);
    int x = in.nextInt();

    if(x==1){
        System.out.println("Choose a denomination");
        int y = in.nextInt();
        in.nextLine();
        if(y==1){
            System.out.println("Which person appears on the 1 bill?");
            String answer = in.nextLine();
            if(answer.equals("Washington")){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }


        else if(y==10){
            System.out.println("Which person appears on the 10 bill?");
            String answer = in.nextLine();
            if(answer.equals("Hamilton")){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else if(y==100){
            System.out.println("Which person appears on the 100 bill?");
            String answer = in.nextLine();
            if(answer.equals("Franklin")){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else{
            System.out.println("That is an invalid number.");
        }
    }
    else if(x==2){
       System.out.println("Choose a name");
        String y = in.nextLine();
        in.nextLine();
        if(y.equals("Washington")){
            System.out.println("Which denomination does this name appear on?");
            int answer = in.nextInt();
            if(answer==1){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }


        else if(y.equals("Hamilton")){
            System.out.println("Which denomination does this name appear on");
            int answer = in.nextInt();
            if(answer==10){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else if(y.equals("Franklin")){
            System.out.println("Which denomination does this name appear on");
            int answer = in.nextInt();
            if(answer==100){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else{
            System.out.println("That is an invalid number.");
        }
    } 
}

问题出在 x==2 段上。 x==1 工作正常。

Answer 1

问题不在于看似额外的in.nextLine()。

我建议您将所有 in.nextInt() 更改为 in.nextLine() 然后将它们解析为实际情况类型如 int

示例:

int answer = Integer.parseInt(in.nextLine());

建议更改的原因:当您使用 nextInt() 时，下一行仍然会停留在那里，直到您执行额外的 nextLine( ) 清除它。

为了防止此类问题，建议使用 nextLine() 接收所有输入，然后将其解析为实际类型(int、double ..等)。

这也是 Microsoft 处理 C# 中整数输入的方式。

<小时/>

编辑后的工作代码:

public static void main(String[] args) {

    System.out.println("Type 1 to enter a denomination, 2 to enter a last name");
    Scanner in = new Scanner(System.in);
    int x = Integer.parseInt(in.nextLine());

    if(x==1){
        System.out.println("Choose a denomination");
        int y = Integer.parseInt(in.nextLine());
        in.nextLine();
        if(y==1){
            System.out.println("Which person appears on the 1 bill?");
            String answer = in.nextLine();
            if(answer.equals("Washington")){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }


        else if(y==10){
            System.out.println("Which person appears on the 10 bill?");
            String answer = in.nextLine();
            if(answer.equals("Hamilton")){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else if(y==100){
            System.out.println("Which person appears on the 100 bill?");
            String answer = in.nextLine();
            if(answer.equals("Franklin")){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else{
            System.out.println("That is an invalid number.");
        }
    }
    else if(x==2){
       System.out.println("Choose a name");
        String y = in.nextLine();
        //in.nextLine();
        if(y.equals("Washington")){
            System.out.println("Which denomination does this name appear on?");
            int answer = Integer.parseInt(in.nextLine());
            if(answer==1){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }


        else if(y.equals("Hamilton")){
            System.out.println("Which denomination does this name appear on");
            int answer = Integer.parseInt(in.nextLine());
            if(answer==10){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else if(y.equals("Franklin")){
            System.out.println("Which denomination does this name appear on");
            int answer = Integer.parseInt(in.nextLine());
            if(answer==100){
                System.out.println("That is correct");
            }
            else{
                System.out.println("That is incorrect");
            }
        }
        else{
            System.out.println("That is an invalid number.");
        }
    } 
}