Java:无法访问变量？

Question

所以我在比较主类中声明的两个字符串时遇到了一点问题。我把它弄得一团糟，我真的无法让它工作！问题出在if（）语句中，我在其中比较变量

public class Main {

    public String oldContent = "";
    public String newContent = "";

    public static void main(String[] args) throws InterruptedException {
        Main downloadPage = new Main();
        downloadPage.downloadPage();
        oldContent = newContent;

        for (;;) {
            downloadPage.downloadPage();
            if (!oldContent.equals(newContent)) { // Problem
                System.out.println("updated!");
                break;
            }
            Thread.currentThread().sleep(3000);
        }
    }

    private void downloadPage() {
        // Code to download a page and put the content in newContent.
    }
}

Answer 1

变量位于Main对象内：

public static void main(String[] args) throws InterruptedException {
    Main downloadPage = new Main();
    downloadPage.downloadPage();  // Access them like you accessed the method
    downloadPage.oldContent = downloadPage.newContent;

    for (;;) {
        downloadPage.downloadPage();
        if (!downloadPage.oldContent.equals(downloadPage.newContent)) {
            System.out.println("updated!");
            break;
        }
        Thread.currentThread().sleep(3000);
    }
}

请考虑使用GETSter和SETTER，而不是公开字段。

Answer 2

您可以使用已创建对象的名称（downloadPage）访问以下参数： 在主函数中，仅使用以下名称而不是参数名称：

downloadPage.oldContent
downloadPage.newContent

Answer 3

见non static/ static variable error

Answer 4

变量是实例成员，而for发生在静态方法中。 尝试将实际函数移动到实例方法（不是静态的），或者反过来使数据成员也是静态的