未知的编译错误Java

Question

I have been going through some online exercises in Java, and I can't figure out why this tid-bit of code won't compile.

I am forgetting something obvious I know it.

import java.util.Scanner;

class age {

public static void main (String[] args) {

Scanner keyboard = new Scanner (System.in);

int age;

System.out.println("How old are you?");
age = keyboard.nextInt();
System.out.println("You are " + age);

if (age =< 16) {
    System.out.println("You cannot Vote, Drive or Drink Alcohol");
}

if (age =<16 && <18) {
    System.out.println("You can DRIVE, you may NOT Vote or Drink Alcohol");
}

if (age =>18 && <21) {
    System.out.println("You can Drive and Vote, you may NOT Drink Alcohol");
}
if (age =>21){
    System.out.println("You May Drive, Vote and Drink Alcohol");
}

}
}

Thanks for the replies, The obvious (now) fact that the if statements have to have a variable to test for each condition eg. if (age >=16 && age <18). without the both variables (age) the compiler spat out 17 errors with non-specific error messages.

I will try to make sure to follow convention when naming variables and class names. no need to make it extra complicated.

Thanks again.

import java.util.Scanner;

class age {

public static void main (String[] args) {

Scanner keyboard = new Scanner (System.in);

int aga;

System.out.println("How old are you?");
aga = keyboard.nextInt();
System.out.println("You are " + aga);

if (aga <= 16) {
    System.out.println("You cannot Vote, Drive or Drink Alcohol");
}

if (aga >=16 && aga <18) {
    System.out.println("You can DRIVE, you may NOT Vote or Drink Alcohol");
}

if (aga >=18 && aga <21) {
    System.out.println("You can Drive and Vote, you may NOT Drink Alcohol");
}
if (aga >=21){
    System.out.println("You May Drive, Vote and Drink Alcohol");
}

}
}

I have changed the parameters of the if statements so only one of them can be satisfied, changed the variable age to aga, and re-written the conditions of the if statements to read correctly.

Answer 1

The less than and greater than operators in Java (and frankly, in most programming languages) are <= and >= , respectively, not =< and => like your code currently has.

Additionally, you cannot apply to comparison operators to a single variable/value - you'd need to have two separate conditions with a logical operator between them.

Eg, instead of your current:

if (age =<16 && <18)

You'd need to write:

if (age <= 16 && age < 18)

Note also that this condition is redundant - if an age is less than or equal to 16, it is obviously less than 18, so the condition could be simplified to

if (age <= 16)

Answer 2

You forget to import Scanner class from java.util package and also using the less than operator in wrong way. Below is the corrected snippet:

import java.util.Scanner;

class age {

    public static void main(String[] args) {

        Scanner keyboard = new Scanner(System.in);

        int age;

        System.out.println("How old are you?");
        age = keyboard.nextInt();
        System.out.println("You are " + age);

        if (age <= 16) {
            System.out.println("You cannot Vote, Drive or Drink Alcohol");
        }

        if (age <= 16 && age < 18) {
            System.out
                    .println("You can DRIVE, you may NOT Vote or Drink Alcohol");
        }

        if (age <= 18 && age < 21) {
            System.out
                    .println("You can Drive and Vote, you may NOT Drink Alcohol");
        }
        if (age <= 21) {
            System.out.println("You May Drive, Vote and Drink Alcohol");
        }

    }
}

Answer 3

As the users have mentioned before, you used your operator incorrectly. One other thing worth nothing here is that the way you have set up your if statements allows multiple executions (which I'm not sure is what you wanted). For example, if age were 10, all four println statements would be executed because it satisfies every single condition in all of the if statements. Consider using 'if-else' statements if this is not your intention.

Answer 4

You have to show the error message when you post these but even without that there are some pretty glaring errors:

1. The form of your tests should be >=, <=, etc (and not =>, =<)
2. if (age =<16 && <18) is really just if (a < 16) but if you want to have 2 conditions it has to be if (age =<16 && a<18)
3. It's bad form to have a variable inside your class with the same name as your class.