如下代码,输出结果是什么? public class Test { public int aMethod() { static int i = 0; i++; return i; } public static void main (String args[]) { Test test = new Test(); test.aMethod(); int j = test.aMethod(); System.out.println(j); } }

时间: 2024-01-13 14:05:38 浏览: 27
这段代码是有语法错误的,因为在方法 aMethod() 中定义了一个静态变量 i,但是静态变量不能在方法中定义,只能在类中定义。 如果将静态变量 i 定义在类中,则输出的结果是 2。因为第一次调用 aMethod() 方法时,i 的值从 0 变为 1,并将 1 返回;第二次调用 aMethod() 方法时,i 的值从 1 变为 2,并将 2 返回。最后输出的 j 的值是 2。以下是修正后的代码: ``` public class Test { static int i = 0; public int aMethod() { i++; return i; } public static void main (String args[]) { Test test = new Test(); test.aMethod(); int j = test.aMethod(); System.out.println(j); } } ```
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public class Test { public int aMethod() { static int i = 0; i++; return i; } public static void main (String args[]) { Test test = new Test(); test.aMethod(); int j = test.aMethod(); System.out.println(j); } }

这段代码有语法错误,无法通过编译。静态变量不能在方法内部声明。正确的写法应该是将静态变量 i 声明在方法外部,如下所示: ``` public class Test { static int i = 0; public int aMethod() { i++; return i; } public static void main(String[] args) { Test test = new Test(); test.aMethod(); int j = test.aMethod(); System.out.println(j); } } ``` 此时输出结果为 2,因为 i 的值在两次调用 aMethod 方法时分别增加了 1。

以下程序运行结果正确的是:【 】 class Base { public void method() { System.out.println("不带参Base"); } } public class Sub extends Base { public void method() { System.out.println("不带参Sub"); } public int method(int a) { System.out.println("带参Sub"); return 0; } public static void main(String[] args) { Sub test = new Sub(); test.method(); test.method(0); } }

以下程序运行结果是正确的: 输出结果为: 不带参Sub 带参Sub 解析: Sub类继承了Base类,并重写了method方法。在Sub类中,定义了两个method方法,一个是不带参数的方法,一个是带参数的方法。在main方法中,创建了Sub类的对象test,并分别调用了不带参数和带参数的method方法。由于Sub类重写了method方法,因此调用不带参数的method方法时,会调用Sub类中的方法,输出"不带参Sub";调用带参数的method方法时,会调用Sub类中的带参数的方法,输出"带参Sub"。因此,程序运行结果是正确的。

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use java language ,In this project you need to write a book lending system for a Library. The system has different roles for registered users. There are two types of user roles: borrower and lender. Write an IUser interface for library users, with the following UML specification: +----------------------------------+ | <<interface>> | | IUser | +----------------------------------+ | + getName(): String | | + getBook(): int | | + moreBook(int number): void | +----------------------------------+ and a User class that implements IUser and has the following UML specification: +-----------------------------------+ | User | +-----------------------------------+ | - name: String | | - book: int | +-----------------------------------+ | + User(String name, int book) | | + getName(): String | | + getBook(): int | | # setBook(int book): void | | + moreBook(int number): void | | + testUser(): void | +-----------------------------------+ The name instance variable indicates the user name. The book instance variable indicates the number of books borrowed by the user. The setBook method changes the number of books borrowed by the user. The setBook method is protected, not public. This means that only subclasses of the User class can use the setBook method. All the other classes in the system cannot use the setBook method, so they cannot change the number of books borrowed by a user. The purpose of the moreBook method is to increase the number of books borrowed or lent by the user (depending on what kind of user it is) by the number given as argument to the method. The moreBook method of the User class is abstract, since we do not know what kind of role the user is (a borrower borrows books from other users and a lender lend books to other users). Also add to your program a Test class to test your User class. public class Test { public static void main(String[] args) { User.testUser(); } }

帮我写出以下java代码:Add a class Bubble that extends Shape. The Bubble class has an instance variable called radius of type double that represents the radius of the bubble. The constructor of the Bubble class takes an x and a y as arguments, which represent the position of the new bubble. The radius of a new bubble is always 10 and never changes after that. The isVisible method indicates whether the bubble is currently visible inside a window of width w and height h (position (0, 0) is in the upper-left corner of the window). The bubble is considered visible if at least one pixel of the bubble is visible. Therefore a bubble might be visible even when its center is outside the window, as long as the edge of the bubble is still visible inside the window. The code of the isVisible method is a little bit complex, mostly because of the case where the center of the circle is just outside one of the corners of the window. So here is the code of the isVisible method, which you can directly copy-paste into your assignment: // Find the point (wx, wy) inside the window which is closest to the // center (x, y) of the circle. In other words, find the wx in the // interval [0, w - 1] which is closest to x, and find the wy in the // interval [0, h - 1] which is closest to y. // If the distance between (wx, wy) and (x, y) is less than the radius // of the circle (using Pythagoras's theorem) then at least part of // the circle is visible in the window. // Note: if the center of the circle is inside the window, then (wx, wy) // is the same as (x, y), and the distance is 0. public boolean isVisible(int w, int h) { double x = getX(); double y = getY(); double wx = (x < 0 ? 0 : (x > w - 1 ? w - 1 : x)); double wy = (y < 0 ? 0 : (y > h - 1 ? h - 1 : y)); double dx = wx - x; double dy = wy - y; return dx * dx + dy * dy <= radius * radius; } The isIn method indicates whether the point at coordinates (x, y) (which are the arguments of the method) is currently inside the bubble or not. The edge of the bubble counts as being inside of the bubble. HINT: use Pythagoras's theorem to compute the distance from the center of the bubble to the point (x, y). The draw method uses the graphics object g to draw the bubble. HINT: remember that the color of the graphics object g is changed in the draw method of the superclass of Bubble. Also add a testBubble method to test all your methods (including inherited methods, but excluding the isVisible method, which I provide, and excluding the draw method since it requires as argument a graphics object g that you

根据以下要求:Instead of using a binary file to save the arraylist of points, change the savaData method and the constructor of the Model class to use a database to write / read the coordinates of all the points. Use XAMPP and phpMyAdmin to create a database called "java" with a table called "points" that has two integer columns x and y (in addition to the ID primary key). Hint: make sure you delete all the old point coordinates from the database before inserting new ones. Hint: use phpMyAdmin to check what is stored in the database. Use the Test class to run all the tests for the software and check that all the tests still work. Use the Start class to run the software and check that closing the software correctly saves the point coordinates in the database (use phpMyAdmin to check the content of the database). Run the software again and check that all the points from the previous run are correctly displayed,修改下述代码:public class Model implements Serializable { private ArrayList points; private ArrayList<ModelListener> listeners; private static final String FILE_NAME = "points.bin"; public Model() { points = new ArrayList(); listeners = new ArrayList<ModelListener>(); // Read points from file if it exists File file = new File(FILE_NAME); if (file.exists()) { try { ObjectInputStream in = new ObjectInputStream(new FileInputStream(file)); points = (ArrayList) in.readObject(); in.close(); } catch (IOException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } } public void addListener(ModelListener l) { listeners.add(l); } public ArrayList getPoints() { return points; } public void addPoint(Point p) { points.add(p); notifyListeners(); // points changed so notify the listeners. saveData(); // save point to file } public void clearAllPoints() { points.clear(); notifyListeners(); // points changed so notify the listeners. saveData(); // save empty list to file } public void deleteLastPoint() { if (points.size() > 0) { points.remove(points.size() - 1); notifyListeners(); // points changed so notify the listeners. saveData(); // save updated list to file } } private void notifyListeners() { for (ModelListener l : listeners) { l.update(); // Tell the listener that something changed. } } public int numberOfPoints() { return points.size(); } public void saveData() { try { ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(FILE_NAME)); out.writeObject(points); out.close(); } catch (IOException e) { e.printStackTrace(); } }

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