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# instanceof  operator

* Summary

1. Check instanceof whether type transition is possible or not.

2\. Type transition

3\. instanceof parent returns true, but it does NOT mean fe is Object or Car!

4\. **Why doing reference type transition?** By modifying reference type variable(remote control), able to **control the number of usable members.**

```java
FireEngine f = new FireEngine();//the number of usable members : 5
Car c = (Car)f;//CONTROL the number of usable members:4.
```

1. Check the type transition is possible. if it is possible, return true.

Before type transition, MUST check instanceof before type transition.

```java
//To use the function(method) of instance.
//Car type 'c' CANNOT call water();

//Change 
void doWork(Car c) {
    if(c instanceof FireEngine) {
        FireEngine fe = (FireENgine)c;
        fe.water();
    }
}
```

instanceof for parent and itself returns true.

FireEngine < Car < Object

fe instanceof Object/Car is true, but it does NOT mean fe is Object or Car. But it means type transition is possible.

```java
FireEngine fe = new FireEngine();
System.out.println(fe instanceof Object);.//fe indicates Object?true.
System.out.println(fe instanceof Car);//fe indicates Car?true.
System.out.println(fe instanceof FireEngine);//fe indicates FireEngine?true.(itself)
```