Think in java P202Once you learn about polymorphism, you can begin to think that everything happens polymorphically. However, only ordinary method calls can be polymorphic.
For example, if you access a field directly, that access will be resolved at compile time, as the following example demonstrates.
一旦你学了多态，你就开始想象所有的东西都可以多态。然而，只有普通的方法可以多态化。例如，如果你直接访问一个字段，该访问将在编译时解决。
class Super {
public int field = 0;
public int getField() { return field; }
}
class Sub extends Super {
public int field = 1;
public int getField() { return field; }
public int getSuperField() { return super.field; }
}
public class FieldAccess {
public static void main(String[] args) {
Super sup = new Sub(); // Upcast
System.out.println("sup.field = " + sup.field +
", sup.getField() = " + sup.getField());
Sub sub = new Sub();
System.out.println("sub.field = " +
sub.field + ", sub.getField() = " +
sub.getField() +
", sub.getSuperField() = " +
sub.getSuperField());
}
}
输出：
sup.field = 0, sup.getField() = 1
sub.field = 1, sub.getField() = 1, sub.getSuperField() = 0
所以多态只能用于普通方法啦。
虽然这似乎可能是一个令人困惑的问题，但实际上它实际上并没有出现。因为实际开发中我们都将变量设为私有啦。
当果然还有静态方法喽
class StaticSuper { public static String staticGet() { return "Base staticGet()"; } public String dynamicGet() { return "Base dynamicGet()"; } } class StaticSub extends StaticSuper { public static String staticGet() { return "Derived staticGet()"; } public String dynamicGet() { return "Derived dynamicGet()"; } } public class StaticPolymorphism { public static void main(String[] args) { StaticSuper sup = new StaticSub(); // Upcast System.out.println(sup.staticGet()); System.out.println(sup.dynamicGet()); } }
输出：
Base staticGet()
Derived dynamicGet()
静态方法只和类有关啦，和某个对象没有关系啦。
原文：http://www.cnblogs.com/alway-july/p/7505322.html