Question

对于我正在进行的练习，我有三个方法，所有isEven都测试一个值并返回true或false。一个isEven是一个实例方法，另外两个是静态方法，每个方法都有一个参数。如果我创建一个新的testClass，并在main方法中运行方法，则实例isEven方法工作正常，但是当我尝试使用静态isEven方法时，我得到一个符号未找到错误。但是，如果我在实际的app类中创建main方法并在那里运行它，重载的方法将起作用。为什么会这样？静态方法不能在另一个类中运行吗？使用的方法如下。

public class MyInteger {
    private int value;
    public boolean isEven() {
        if(this.value % 2 == 0) {
            System.out.println(value + " is an even number.");
            return true;
        }
        else {
            System.out.println(value + " is not an even number.");
            return false;
        }
    }

    public static boolean isEven(int value) {
        if(value % 2 == 0) {
            System.out.println(value + " is an even number.");
            return true;
        }
        else {
            System.out.println(value + " is not an even number.");
            return false;
        }
    }

    public static boolean isEven(MyInteger value) {
        if(value.value % 2 == 0) {
            System.out.println(value.value + " is an even number.");
            return true;
        }
        else {
            System.out.println(value.value + " is not an even number.");
            return false;
        }
    }
}
class testMyInteger {
    public static void main(String[] args) {
        MyInteger val1 = new MyInteger(2);
        int val = 2;
        System.out.println("The value of this object is " + val1.getValu());
        val1.isEven();
        val1.isOdd();
        val1.isPrime();
        isEven(val1);
    }
}

Answer 1

让我们来看看你的代码：

public static void main(String[] args) {
    MyInteger val1 = new MyInteger(2);
    int val = 2;
    System.out.println("The value of this object is " + val1.getValu());
    val1.isEven();
    val1.isOdd();
    val1.isPrime();
    isEven(val1); // <-- here is the problem.
}

static方法与免费方法不同。您仍然需要使用类或通过该类的实例来调用它们。

E.g：

 public static void main(String[] args) {
    MyInteger val1 = new MyInteger(2);
    int val = 2;

    MyInteger.isEven(val1);
    val1.isEven(val1);

    MyInteger.isEven(val);
    val1.isEven(val);
}

Answer 2

这里有几个问题。他们在评论中有解释，但我会在这里列出：

我在帖子中没有看到构造函数（在撰写本文时）

你的main（）方法在同一个java文件中，但不是同一个类。它们是两个非常不同的东西。

public class MyInteger {
    // Not included in post
    private int value;
    // Not included in post
    public MyInteger(int i) {
        value = i;
    }

    public boolean isEven() {
        if (this.value % 2 == 0) {
            System.out.println(value + " is an even number.");
            return true;
        } else {
            System.out.println(value + " is not an even number.");
            return false;
        }
    }

    public static boolean isEven(int value) {
        if (value % 2 == 0) {
            System.out.println(value + " is an even number.");
            return true;
        } else {
            System.out.println(value + " is not an even number.");
            return false;
        }
    }

    public static boolean isEven(MyInteger value) {
        if (value.value % 2 == 0) {
            System.out.println(value.value + " is an even number.");
            return true;
        } else {
            System.out.println(value.value + " is not an even number.");
            return false;
        }
    }

}

class testMyInteger {
    public static void main(String[] args) {
        MyInteger val1 = new MyInteger(2);
        int val = 2;
        //System.out.println("The value of this object is " + val1.getValue()); // mispelled here, Not declared anyways
        val1.isEven();
        // these are not declared
        //val1.isOdd();
        //val1.isPrime();

        // Not inside of the 'MyInteger class, therefor not able to be called without static reference of MyInteger.isEvent
        //isEven(val1);
        MyInteger(val1);
    }
}

重载的静态方法没有在其他类中运行？

2 个答案: