我刚才注册了，尽管自从我从事计算机编程以来就一直在充分利用这个站点，我一直在自学并考虑我的一点爱好。

我确实在寻找类似的问题，但实际上我找不到我想要的答案。
现在，您已经意识到，在Java(这是我建议使用的语言)中，在需要时声明和实例化变量被认为是良好的编程习惯，请考虑以下几行:

class MyClass {
    void myMethod() {
        AnotherClass myObject = new AnotherClass();
        myObject.doStuff();
    }
}

    public class DataBase {

    private static String buf, retString = "\n";
    private static File file = new File("test.txt");

    public static void readText(JTextArea area) {   
        try {
            FileReader fr = new FileReader (file);
            BufferedReader br = new BufferedReader(fr);
            while ((buf = br.readLine()) != null) {
                area.append(buf); 
                area.append(retString);
            }
            br.close(); 
            fr.close();
        }
        catch (IOException e) {
            System.out.println("Exception: " + e);
        }
    }

    public static void writeText(JTextArea area) {
        try {
            FileWriter fw = new FileWriter (file);
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write(area.getText());
            bw.close(); 
            fw.close();
        }
        catch (IOException e) {
            System.out.println("Exception: " + e);
        }
    }
}

最佳答案

是的，如果您调用myMethod() 10次，它将创建10个唯一且独立的对象。
new关键字完全按照其在锡 jar 上的说明进行操作，无论是否已经存在，它都会创建一个全新的对象。它将创建一个新对象，并将对该对象的引用填充到已给定的变量中，从而覆盖该变量保存的所有先前值(对象)。

Is the myObject variable reallocated every time?

In a nutshell: should I write code like that only if I plan to invoke that method only once?

public class DataBase {

private static String buf, retString = "\n"; // buf & retString - created
private static File file = new File("test.txt"); // file - created

public static void readText(JTextArea area) {   
    try {
        FileReader fr = new FileReader (file); // fr (FileReader) - created
        BufferedReader br = new BufferedReader(fr); // br (BufferedReader) - created
        while ((buf = br.readLine()) != null) {
            area.append(buf); 
            area.append(retString);
        }
        br.close();
        fr.close();
    } // fr (FileReader & br (BufferedReader) - destroyed
    catch (IOException e) {
        System.out.println("Exception: " + e);
    }
}

public static void writeText(JTextArea area) {
    try {
        FileWriter fw = new FileWriter (file); // fw (FileWriter) - created
        BufferedWriter bw = new BufferedWriter(fw); // bw (BufferedWriter) - created
        bw.write(area.getText());
        bw.close(); 
        fw.close();
    } // fw & bw - destroyed
    catch (IOException e) {
        System.out.println("Exception: " + e);
    }
}
} // buf, retString and file - Still exist as long as the object exists

private static String buf, retString = "\n"; // valid
private static File file = new File("test.txt"); // valid

FileReader fr = new FileReader (file); // valid
BufferedReader br = new BufferedReader(fr); // valid
FileWriter fw = new FileWriter (file); // valid
BufferedWriter bw = new BufferedWriter(fw); // valid

FileReader fr = new BufferedReader(fr); // Is not valid!

关于java - 'new'关键字在Java中实际上有什么作用，应该避免创建新对象吗？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7019754/