如何使用System.out.println打印报告错误的消息，该消息显示无效参数但不存储该参数？

Question

I need to print out the invalid parameter in the System.out.println message without storing it.

If the parameter is not between 1500 and 2000, I need to print a message saying "1400 is too early" or "2500 is too late".

I wrote this but unfortunately it only prints the default parameter for the integer (0):

    /**
     /* @param newModelYear is the model year of the car; invaild if the year is not in range between 1500 and 2000
     /*/
    public void setModelYear(int newModelYear){
        if ((modelYear <1500) && (modelYear >2000)) {
         modelYear=newModelYear;
        }
        else {
            System.out.println(getModelYear + "sorry it is too early!");
        }
     }

Answer 1

To sum it up, it should be:

public void setModelYear(int newModelYear){
    if ( newModelYear < 1500 ) {
        System.out.println(newModelYear + ": sorry it is too early!");
    } else if ( newModelYear > 2000)) {
        System.out.println(newModelYear + ": sorry it is too late!");
    } else {
        modelYear=newModelYear;
    }
 }

Explanation: instead of

        System.out.println(getModelYear + "sorry it is too early!");

write

        System.out.println(newModelYear + "sorry it is too early!");

This uses the passed-in variable newModelYear .

And consider that you need >= 1500 instead of <1500 and <= 2000 instead of >2000 , as @JB Nizet said.

Thirdly, you might want to compare

    if ((newModelYear >= 1500) && (newModelYear <= 2000)) {

instead of

    if ((modelYear <1500) && (modelYear >2000)) {

Answer 2

You have your signs wrong. Change

if ((modelYear <1500) && (modelYear >2000)) {
 modelYear=newModelYear;
}

To

if ((modelYear > 1500) && (modelYear < 2000)) {
 modelYear=newModelYear;
}

Remember, > means "greater than". < means "less than"

These signs are called "Boolean operators". They take they left and right sides of the operator, return true or false. The < symbol takes the left number, and checks if the right number is bigger. If so, it returns true. If it isn't it returns false.

1 < 2

Returns true, because the number 1, on the left is less than the number 2, on the right.

if statements work using only true or false values. Everything you use inside it returns one of these values. Boolean operators take the values you use and turn them into boolean values that the if statement can use.

Answer 3

I think using a try catch block (maybe more than one) to send the error you catch here to your parent code. See the below link for more details.

Java: Proper way to throw and catch an exception to validate input

Answer 4

The below code will resolve your problem

  public void setModelYear(int newModelYear){
       if(newModelYear < 1500){
          System.out.println("It is too early");
       }
        else if(newModelYear > 2500){
          System.out.println("It is too late");
       }
       else{
          modelYear=newModelYear;
       }
     }

Answer 5

There is an easier way to tackle this problem:

/**
 /* @param newModelYear is the model year of the car; invaild if the year is not in range between 1500 and 2000
 /*/
public boolean setModelYear(int newModelYear){
    if(newModelYear < 1500){
        // Too old
        System.out.printf("Error: %d is too old.%n", newModelYear);
        return false;
    }else if(newModelYear > 2000){
        // Too new
        System.out.printf("Error: %d is too new.%n", newModelYear);
        return false;
    }else{
        // Just right (In range)
        // Set the object's model year to the new value
        modelYear = newModelYear;
        return true;
    }
 }

Hopefully that will help you. There's not much to say, but if you have any questions about it, feel free to ask.

Edit : I added a return to the function. The code can be used without a return ( public void setModelYear(...) ), but I decided to change the function to return a boolean. If the newModelYear is valid and modelYear is changed, the function will return true to inform the calling function that the update was successful and the input provided was valid. Else, if the newModelYear is invalid, the code will still output an error to the console just like before, but it will now return false as well. If the returned value is false, this informs the caller that the input was not valid and modelYear was not changed.

Answer 6

This should solve your problem.

You just have to check if modelYear is less than 1500 or greater than 2000 separately in order to print their respective errors, and then set the new value if the value is between 1500 and 2000.

public void setModelYear(int newModelYear){
    if (modelYear < 1500) {
        System.out.println(newModelYear + "sorry it is too early!");
    } else if (modelYear > 2000) {
        System.out.println(newModelYear + "sorry it is too late!");
    } else {
        modelYear = newModelYear;
    }
 }