java 当两个类实现相同的接口时
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When two classes implement the same interface
提问by Madrugada
Suppose there are 2 classes which implement a same interface and the methods from that interface. If I call a method directly from the interface, what is what decides which implementation will be returned (from first or second class) ?
假设有 2 个类实现了相同的接口和来自该接口的方法。如果我直接从接口调用一个方法，是什么决定将返回哪个实现（从第一类或第二类）？
回答by Bill the Lizard
You don't call a method directly from an interface, you call it on a reference that points to an instance of a class. Whichever class that is determines which method gets called.
您不直接从接口调用方法，而是在指向类实例的引用上调用它。哪个类决定调用哪个方法。
回答by Michael Besteck
package test;
public interface InterfaceX {
int doubleInt(int i);
}
package test;
public class ClassA implements InterfaceX{
@Override
public int doubleInt(int i) {
return i+i;
}
}
package test;
public class ClassB implements InterfaceX{
@Override
public int doubleInt(int i) {
return 2*i;
}
}
package test;
public class TestInterface {
public static void main(String... args) {
new TestInterface();
}
public TestInterface() {
InterfaceX i1 = new ClassA();
InterfaceX i2 = new ClassB();
System.out.println("i1 is class "+i1.getClass().getName());
System.out.println("i2 is class "+i2.getClass().getName());
}
}
回答by Gilbert Le Blanc
You define the instance of an interface by executing the constructor of a concrete class that implements the interface.
您可以通过执行实现接口的具体类的构造函数来定义接口的实例。
Interface interface = new ConcreteClass();
回答by Vishy
interface cannot have body/definition for the method. All the methods are abstract. You cannot define method body, hence you cannot call any method from interface.
接口不能有方法的主体/定义。所有的方法都是抽象的。你不能定义方法体，因此你不能从接口调用任何方法。
