以下是您的问题的最小可重现示例：

public class Input {

    static Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
        provideInput();
    }
    static String input;

    public static void provideInput() {
        System.out.println("Read name:" );
        input = scanner.next();
        if ( input.equals("false")) {
            provideInput(); // here you recursively call the same method again. That does not mean that the original execution ends.
        }
        System.out.println("input = " + input);
    }
}

如果我输入"false"，第二次输入"true"，它会给我

input = true
input = true

作为输出。
如果只需要一次，请将print语句移到调用方法：

public class Input {

    static Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
        provideInput();
        System.out.println("input = " + input);
    }
    static String input;

    public static void provideInput() {
        System.out.println("Read name:" );
        input = scanner.next();
        if ( input.equals("false")) {
            provideInput();
        }
    }
}

这将仅在该方法的原始执行完成后打印。

confirmDetails()方法正在调用calResult()，这将导致额外的输出。每次调用calResult()时，您将有一行输出。由于confirmDetails()由calResult()调用，并且它本身可能调用calResult()，因此您将生成额外的输出行。

calResult() {
  ... stuff happen ...
  confirmDetails()
  output()
}

confirmDetails() {
  ... stuff happens ...
  calResults(..)
}

你需要稍微重新组织你的代码。限制每个方法的责任是有帮助的。考虑为每个操作编写方法，并且你的入口点管理控制流。例如。

public void calResult() {
  while (true) {
    getUserInput();
    if (confirmDetails()) {
      break;
    }
  }
  double aggregate = calculateAggregate();
  emitAggregate(aggregate);
}

它执行了两次，因为confirmDetails();是从同一个calResult()调用的，在confirmDetails();被调用后，你要打印这个值，所以一旦第一次调用被执行，控制流就会回到第一次调用，并执行剩下的代码，也就是再次打印这个值。
建议将确认调用移为主类。
这是我写的一个例子，输入来自主类本身，但这会给予你一个更好的想法。

public class Calculate {

    private String name;
    private float jamb, postUtme, aggregate;

    public Calculate(String name, float jamb, float postUtme) {
        this.name = name;
        this.jamb = jamb;
        this.postUtme = postUtme;
        this.aggregate = (jamb / 8) + (postUtme / 2);
    }

    public void calResult() {
        System.out.println("Dear " + name + " your aggregate is " + aggregate);
    }

   //Getters & Setters
}

主类

public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String name = "PlaceHolderValue";
        int jamb = 0;
        int postUtme = 0;
        boolean retry = true;
        do {
            System.out.println("Enter your name");
            name = input.next();

            System.out.println("Enter Jamb score");
            jamb = input.nextInt();

            System.out.println("Enter PostUtme score");
            postUtme = input.nextInt();

            System.out.println("""
                    Correct??
                        \t1 to confirm
                        \t2 to re-enter""");
            int confirmD = input.nextInt();
            retry = confirmD == 2;
        } while (retry);

        input.close();

        Calculate c = new Calculate(name, jamb, postUtme);
        c.calResult();
    }

下面的代码只是使用Scanner.nextLine()，并使用String.matches()方法和小Regular Expressions验证所有用户输入。
confirmDetails()方法实际上被重写以返回布尔值（true表示确认，false表示重写）。

• • 代码中使用的正则表达式：**
• "-?\\d+"输入是否匹配有符号或无符号整数值的字符串表示;
• "[12]"输入是否与1或2的无符号整数值的字符串表示形式匹配。
• • 代码：**

Scanner input = new Scanner(System.in);
String final LS = System.lineSeparator();

public void calResult() {
    String name = "";
    int jamb, postUtme;
    double aggregate = 0.0d;
            
    boolean validInfo = false;
    while (!validInfo) {
        // Name
        String aName = "";
        while (aName.isEmpty()) {
            System.out.print("Enter your name: -> ");
            aName = input.nextLine().trim();
            // Entry Validation: Is the entry empty?  
            if (aName.isEmpty()) {
                // Yes...inform User and allow for retry...
                System.out.println("Invalid Entry! You must enter a valid name! "
                                 + "Try again..." + LS);
                aName = "";
            }
        }
        name = aName;
        
        // Jamb
        String jam = "";
        while (jam.isEmpty()) {
            System.out.print("Enter Jamb score: -> ");
            jam = input.nextLine().trim();
            /* Entry Validation: Is the entry a string representation of
               a signed of unsigned integer value?           */
            if (!jam.matches("-?\\d+")) {
                // No...Inform User and allow retry:
                System.out.println("Invalid Entry! (" + jam + ") You must enter "
                                 + "a valid Jamb score! Try again..." + LS);
                jam = "";
            }
        }
        jamb = Integer.parseInt(jam);
        
        // PostUtime
        String postUt = "";
        while (postUt.isEmpty()) {
            System.out.print("Enter PostUtime score: -> ");
            postUt = input.nextLine().trim();
            /* Entry Validation: Is the entry a string representation of
               a signed of unsigned integer value?           */
            if (!postUt.matches("-?\\d+")) {
                // No...Inform User and allow retry:
                System.out.println("Invalid Entry! (" + postUt + ") You must enter "
                                 + "a valid PostUTime score! Try again..." + LS);
                postUt = "";
            }
        }
        postUtme = Integer.parseInt(postUt);
        aggregate = ((double)(jamb / 8.0d) + (double)(postUtme / 2.0d));
        System.out.println();
        
        // Confirm Entry Details:
        validInfo = confirmDetails();
    }
    
    System.out.println();
    System.out.println("Dear " + name + " your aggregate is " + aggregate);
}

public boolean confirmDetails() {
    String confirmD = "";
    while (confirmD.isEmpty()) {
        System.out.println("Is the above information Correct?");
        System.out.println("  1) To confirm");
        System.out.println("  2) To re-enter");
        System.out.print("Choice: -> ");
        confirmD = input.nextLine().trim();
        if (!confirmD.matches("[12]")) {
            System.out.println("Invalid Menu Choice! (" + confirmD + ") "
                             + "Try again..." + LS);
            confirmD = "";
        }
    }
    return !confirmD.equals("2");
}