Question

当我想将对象的名称设置为另一个类时，我遇到了问题，因为我一直收到 NullPointerException ，而且我不太确定如何修复此错误。

以下是一个例子：

头等舱：

//Just excuse the Vehicle class, it's just an example
private Vehicle[] car;
private int number = 1;
private int count = 0;

public store Display()
{
    car = new Vehicle[number];
}

public void setVehicleName(String name)
{
    car[count].setName(name);
}
public String getVehicleName()
{
    return car[count].setName(name);
}

第二课：

//So, I have radio buttons, so I'll just skip to that code
if (addName.equals(e.getActionCommand()))
{
    name = JOptionPane.showInputDialog(null, "Enter the vehicle name: "); //there is a private String name
    name.toLowerCase(); //automatically converted to lower case
    displayStore.setVehicleName(name); //assume an Display object called 'displayStore'
}

所以，如果有人有想法或知道如何解决它，我将不胜感激。谢谢！

Answer 1

java中的对象数组默认设置为null，如果你这样做

Vehicle [] car = new Vehicle[number];
car[1].setName("Toyota");

您将获得NullPointerException，因为car[1]为空

您需要初始化数组。您可能希望在构造函数中执行此操作

public store Display()
{
    car = new Vehicle[number];
    for(int i=0;i<number;i++) {
        car[i] = new Vehicle();
    }
}

Answer 2

您需要在使用前实例化car [count]。因此，请将此方法替换为：

public store Display()
{
    car = new Vehicle[number];
    for(int i = 0; i < count; i++)
        car[i] = new Vehicle();

    //Return some store type object here or change the type to void
    // Moreover it is better to do initialization/instantiation in the constructor, rather
    // than a separate method
}

Java：NPE在数组元素上调用方法

2 个答案: