hey I need help, I can't see what I did wrong.

So this is the question:

Write a class named GasTank containing:
An instance variable named amount of type double, initialized to 0.
An instance variable named capacity of type double.
A constructor that accepts a parameter of type double. The value of the parameter is used to initialize the value of capacity .
A method named addGas that accepts a parameter of type double . The value of the amount instance variable is increased by the value of the parameter. However, if the value of amount is increased beyond the value of capacity , amount is set to capacity .
A method named useGas that accepts a parameter of type double . The value of the amount instance variable is decreased by the value of the parameter. However, if the value of amount is decreased below 0 , amount is set to 0 .
A method named isEmpty that accepts no parameters. isEmpty returns a boolean value: true if the value of amount is less than 0.1 , and false otherwise.
A method named isFull that accepts no parameters. isFull returns a boolean value: true if the value of amount is greater than capacity-0.1 , and false otherwise.
A method named getGasLevel that accepts no parameters. getGasLevel returns the value of the amount instance variable.
A method named fillUp that accepts no parameters. fillUp increases amount to capacity and returns the difference between the value of capacity and the original value of amount (that is, the amount of gas that is needed to fill the tank to capacity).

Code Java:

---

 public class GasTank{
 
 private double amount = 0;
 private double capacity;
 
public GasTank(double x){
capacity = x;
}
public void addGas(double a){
    amount += a;
       if(amount > capacity){
           amount = capacity;
}
}
public void useGas(double b){
     amount -= b;
        if(amount < 0) {
        amount = 0;
}
}
public boolean isEmpty{
   if (amount < 0.1){
       return true;
}
   else{ return false;
}
}
public boolean isFull(){
 if( amount > capacity - 0.1){ 
return true;
}
else{return false;
}
}
public double getGasLevel(){
return amount;
}
public double fillUp(){
    double difference = capacity - amount;
         amount = capacity
     return difference;
 
}
}

---

How do you know something is wrong?

The compiler said so but now I know why. i forgot a ; and ().
minor problem :)

Glad you've got it solved. A suggestion though the next time you post a similar question: please post the complete error messages and indicate which line(s) cause the errors.