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Legal Studies如何透過 Java 中的介面物件訪問派生類成員變數？
當您嘗試用子類物件儲存超類的引用變數時，只能使用此物件訪問超類的成員，如果您嘗試使用此引用訪問派生類的成員，則會收到編譯時錯誤。
示例
interface Sample {
void demoMethod1();
}
public class InterfaceExample implements Sample {
public void display() {
System.out.println("This ia a method of the sub class");
}
public void demoMethod1() {
System.out.println("This is demo method-1");
}
public static void main(String args[]) {
Sample obj = new InterfaceExample();
obj.demoMethod1();
obj.display();
}
}輸出
InterfaceExample.java:14: error: cannot find symbol obj.display(); ^ symbol: method display() location: variable obj of type Sample 1 error
如果您需要使用超類的引用訪問派生類的成員，則需要使用引用運算子轉換引用。
示例
interface Sample {
void demoMethod1();
}
public class InterfaceExample implements Sample{
public void display() {
System.out.println("This is a method of the sub class");
}
public void demoMethod1() {
System.out.println("This is demo method-1");
}
public static void main(String args[]) {
Sample obj = new InterfaceExample();
obj.demoMethod1();
((InterfaceExample) obj).display();
}
}輸出
This is demo method-1 This is a method of the sub class
更新於： 15-Oct-2019
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