Rectangle myRect;
這里沒初始化,改成
Rectangle myRect = new Rectangle(這里輸入構造方法的參數(shù),如果沒參數(shù)就不用輸);
記住,要用到一個實例,必須先實例化一個實例.what is wrong with the following interffacepublic interface something is wrong{ void aMethod(int aValue){System.out.println("hi mom"):}}接口里面的方法，不能有方法體，改成：public interface somethingiswrong{ void aMethod(int aValue){}}somethingiswrong是我打錯了，沒空格public interface somethingiswrong{ void aMethod(int aValue);}