JAVA中的对象引用和类型转换
在对数据进行类型转换之后,我是否仍在处理相同的对象数据 伪代码示例可以是:JAVA中的对象引用和类型转换,java,casting,object-reference,Java,Casting,Object Reference,在对数据进行类型转换之后,我是否仍在处理相同的对象数据 伪代码示例可以是: MyClass car = new MyClass(); car.setColor(BLUE); VW vw = (VW)car; //Expecting to get a blue VW. vw.topSpeed = 220; //Will car have the top speed set now? If topSpeed is a part of the Car object. 在对数据进行类型转换之后,我
MyClass car = new MyClass();
car.setColor(BLUE);
VW vw = (VW)car; //Expecting to get a blue VW.
vw.topSpeed = 220;
//Will car have the top speed set now? If topSpeed is a part of the Car object.
在对数据进行类型转换之后,我是否仍在处理相同的对象数据
对。强制转换将更改对对象的引用类型。它对对象本身没有任何影响
请注意,在您的示例中,要使强制转换成功,VW
必须是MyClass
的超类或接口MyClass
实现,例如:
class MyClass extends VW // or extends something that extends VW
或
具体例子:
class Base {
private int value;
Base(int v) {
this.value = v;
}
public int getValue() {
return this.value;
}
public void setValue(int v) {
this.value = v;
}
}
class Derived extends Base {
Derived(int v) {
super(v);
}
}
然后:
您是否试图同时使用JavaScript和Java小程序,并且需要从彼此访问对象?或者,您只是选择了错误的标签
javascript
,并且只想问一个Java问题吗?对不起,这不是javascript。这是Java,我会修正标记,topSpeed
必须是可访问的,所以如果我最后调用car.getTopSpeed()
,我会得到220?@FireFly3000:是的,如果topSpeed
在代码中设置的地方确实可以访问。我使用getters/setters(最佳实践)添加了一个具体的示例。@T.J.Crowder如果我从代码中删除d
,并启动Base b=new b(1),您的示例为什么不起作用代码>?它认为B不能转换为派生的d。@T.J.CrowderB
将只是一个默认的B
对象。
class Base {
private int value;
Base(int v) {
this.value = v;
}
public int getValue() {
return this.value;
}
public void setValue(int v) {
this.value = v;
}
}
class Derived extends Base {
Derived(int v) {
super(v);
}
}
Derived d = new Derived(1);
System.out.println(d.getValue()); // 1
Base b = d; // We don't need an explicit cast
b.setValue(2); // Set the value via `b`
System.out.println(d.getValue()); // 2 -- note we're getting via `d`
Derived d2 = (Derived)b; // Explicit cast since we're going more specific;
// would fail if `b` didn't refer to a Derived
// instance (or an instance of something
// deriving (extending) Derived)
d2.setValue(3);
System.out.println(d.getValue()); // 3 it's the same object
System.out.println(b.getValue()); // 3 we're just getting the value from
System.out.println(d2.getValue()); // 3 differently-typed references to it