java - 如何在java中实例化一个对象？

Question

我是编程新手，我想知道我在实例化对象时哪里出错了。下面是代码:

public class Testing{
    private int Sample(int c)
    {
        int a = 1;
        int b = 2;
        c = a + b;
        return c;
    }
    public static void main(String []args)
    {
        Sample myTest = new Sample();
        System.out.println(c);
    }
}

Answer 1

您的代码中没有Sample 类。您声明的方法是私有(private)方法。

// private method which takes an int as parameter and returns another int
private int Sample(int c)
{
  int a = 1;
  int b = 2;
  c = a + b;
  return c;
}

对于当前代码段，您需要实例化 Testing 类并使用 Sample 方法。请注意您的类定义前面有关键字 class ，在本例中为 class Testing。

public class Testing{
  private int Sample(int c)
  {
    int a = 1;
    int b = 2;
    c = a + b;
    return c;
 }
  public static void main(String []args)
 {
    Testing t = new Testing(); // instantiate a Testing class object
    int result = t.Sample(1); // use the instance t to invoke a method on it
    System.out.println(result);
 }
}

但这并没有真正意义，您的 Sample 方法总是返回 3 。

你是不是想做这样的事情:

class Sample {
 int a;
 int b;

 Sample(int a, int b) {
    this.a = a;
    this.b = b;
 }

 public int sum() {
    return a + b;
 }
}

public class Testing {
 public static void main(String[] args) {
    Sample myTest = new Sample(1, 2);
    int sum = myTest.sum();
    System.out.println(sum);
 }
}