返回一個接口的Java

Question

我呼籲形狀的界面，我有這樣的方法，我需要實現

public static Shape createShape(String shapeString, int panelWidth, int panelHeight) { 
     Shapes shape = Shapes.valueOf(shapeString); 
     Shape shapey = Shape(shape); 
     Random random = new Random(); 
     int a = random.nextInt(panelWidth); 
     int b = random.nextInt((panelHeight*panelWidth)/(4*a)); 
    } 

我知道我需要返回的形狀，但是我不知道我應該如何這樣做

Answer 1

你是什麼意思「我需要返回一個形狀」？請更清楚。

你不能實例化一個接口，您需要實例化一個實現接口的類，例如：

class Square implements Shape { ... } 

public static Shape createShape(String shapeString, int panelWidth, int panelHeight) { 
    ... 
    return new Square(); 
} 

Answer 2

如果你沒有叫Shape的方法那麼這個聲明是無效的

Shape shapey = Shape(shape); 

而不會編譯...另一方面... ...返回一個接口不像返回一個類一樣，因爲您需要添加return語句和接口，或者一些物體實現接口...

public static Shape createShape(String shapeString, int panelWidth, int panelHeight) { 
     Shapes shape = Shapes.valueOf(shapeString); 
     Shape shapey = Shape(shape); 
     Random random = new Random(); 
     int a = random.nextInt(panelWidth); 
     int b = random.nextInt((panelHeight*panelWidth)/(4*a)); 
     return shapey;//this will do the trick 
    }