输出的方法和问题，为什么我什么也打印不出来？

Question

我正在尝试学习Java技术。

这段代码有什么问题，为什么我不能打印任何东西？

public class CarLoan {
int carLoan = 10000;
int loanLenght = 3; //This will represent a loan length of 3 years.
int interestRate = 5; //This will represent an interest rate of 5% on the loan
int downPayment = 2000; //This will represent the down payment provided by a user for this car purchase.


 public CarLoan() {
    if (loanLenght <= 0 && interestRate <=0) {
      System.out.println("Error! You must take out a valid car loan");
    } else if (downPayment >= carLoan){
      System.out.println("The car can be paid in full");
    }else{
      int remainingBalance = carLoan - downPayment; 
      int months = loanLenght * 12;
      int monthlyBalance = remainingBalance / months; 
      System.out.println("false");
    }
 }



public static void main(String[] args) {
CarLoan masterTask = new masterTask();
System.out.println(CarLoan);
}
}

我尝试更改方法，使其

void

并在其中列出变量。

Answer 1

masterTask

是

CarLoan

类型的变量。当您尝试创建

CarLoan

的实例时，您在语句中误用了它。

public static void main(String[] args) {
CarLoan masterTask = new CarLoan();
System.out.println(masterTask);
}

然后你应该创建一个方法

toString()

来打印对象。

---

你也误解了Java中构造函数的用途。它不用于进行计算。如果你想让一个对象做某事，那么你应该创建一个方法，然后在创建该对象的实例时调用这个方法。变量将对象的实例作为引用，并可用于调用该对象的方法。

public String makeCarLoan() {
  String result;
    if (loanLenght <= 0 && interestRate <=0) {
      result = "Error! You must take out a valid car loan";
    } else if (downPayment >= carLoan){
      result = "The car can be paid in full";
    }else{
      int remainingBalance = carLoan - downPayment; 
      int months = loanLenght * 12;
      int monthlyBalance = remainingBalance / months; 
      result = "false";
    }
    return result;
 }

然后就可以重写之前的代码了

public static void main(String[] args) {
CarLoan carLoan = new CarLoan();
System.out.println(carLoan.makeCarLoan());
}

Answer 2

“...这段代码有什么问题，为什么我不能打印任何东西？...”

您的声明不正确。

CarLoan masterTask = new masterTask();

创建一个新“汽车贷款”。

CarLoan masterTask = new CarLoan();

此外，将 masterTask 发送到 println，而不是 CarLoan。

System.out.println(masterTask);