在同一arrray Java中调用扩展类函数
我有两个类LoanBook&STLoanBook,STLoanBook是LoanBook的一个扩展。它们都位于同一阵列中:在同一arrray Java中调用扩展类函数,java,arrays,methods,Java,Arrays,Methods,我有两个类LoanBook&STLoanBook,STLoanBook是LoanBook的一个扩展。它们都位于同一阵列中: private static final LoanBook[] books = new LoanBook[50]; books[0] = new STLoanBook("B129", "Soil Mechanics", "Engineering"); books[1] = new LoanBook("B238", "Basic Biology", "Science"); b
private static final LoanBook[] books = new LoanBook[50];
books[0] = new STLoanBook("B129", "Soil Mechanics", "Engineering");
books[1] = new LoanBook("B238", "Basic Biology", "Science");
books[2] = new LoanBook("B563", "Company Law", "Business");
books[3] = new STLoanBook("B342", "Cost Accounting", "Business");
books[4] = new LoanBook("B754", "Robotics", "Engineering");
我试图调用仅在STLoanBook中的函数reserve(),当我通过for循环调用它时,它告诉我reserve()不存在,因为它正在检查LoanBook类。如何修复这个问题,因为我已经让循环检查了类SimpleName(),但它似乎仍然出错。救命啊 您可以通过在LoanBook中创建方法
reserve()
来解决此问题,如果不需要执行任何操作,则可以在STLoanBook中扩展此方法。此方法可以:
void reverse() {
return;
}
在借书簿中。您需要
实例和演员:
for( book : books ) {
if( book instanceof STLoanBook ) {
((STLoanBook)book).reserve( );
}
}
您可以在for循环中使用instanceof
运算符和casting
,例如
for (LoanBook book : books) {
if (book instanceof STLoanBook) {
((STLoanBook)book).reserve();
}
}
使用instanceof运算符
示例代码:
A[] books = new A[10];
books[0] = new A();
books[1] = new B();
books[2] = new B();
books[3] = new A();
for (A a:books) {
if (a instanceof B) {
((B) a).reserve();
}
}
首先检查对象是否为STLoanBook的实例。
如果是,则将其强制转换为STLoanBook,然后对其调用reserve函数()
另一个解决方案是为LoanBook编写一个空reserve()函数,并避免使用instanceof,但看起来您并不需要它
for (LoanBook book : books) {
if (book instanceof STLoanBook) {
((STLoanBook)book).reserve();
}
}