JAVA异常总结 ------ 继承

以下是对JAVA异常的继承机制的一些总结。

1. RuntimeException与Exception, Error不同点： 当方法体中抛出非RuntimeException（及其子类）时，方法名必须声明抛出的异常；但是当方法体中抛出RuntimeException（包括RuntimeException子类）时，方法名不必声明该可能被抛出的异常，即使声明了，JAVA程序在某个调用的地方，也不需要try-catch从句来处理异常。

class TestA{
	//compiles fine.we dont need to claim the RuntimeException to be thrown here
	void method(){
		throw new RuntimeException();
	}
}
class TestB{
	void method() throws RuntimeException{
		throw new RuntimeException();
	}
	
	void invokeMethod(){
		//compiles fine. we dont need the try-catch clause here
		method();
	}
}
class TestC{
	
	//compiles error.we need to claim the Exception to be thrown on the method name 
	void method(){
		throw new Exception();
	}
}
class TestD{
	//compiles fine.
	void method() throws Exception{
		throw new Exception();
	}
}

以下所有的相关异常的特性都不包括RuntimeException及其子类。

2. 假如一个方法在父类中没有声明抛出异常，那么，子类覆盖该方法的时候，不能声明异常。

class TestA{
	void method(){}
}
class TestB extends TestA{
	
	//complies error if the method overrided pertaining to the base class doesnt declare throwing exceptions
	void method() throws Exception{
		throw new Exception();
	}
}

3. 假如一个方法在父类中声明了抛出异常，子类覆盖该方法的时候，要么不声明抛出异常，要么声明被抛出的异常继承自它所覆盖的父类中的方法抛出的异常。

class TestA{   
    void method() throws IOException{}   
}   
class TestB extends TestA{   
    //compiles fine if current method does not throw any exceptions   
    void method(){}   
}   
class TestC extends TestA{   
    //compiles fine because InterruptedIOException is inherited from IOException which is thrown by the overrided method of the base class   
    void method() throws InterruptedIOException{}   
}   
class TestD extends TestA{   
    //compiles error because Exception thrown by current method is not inherited from IOException which is thrown by the overrided method of the base class   
    void method() throws Exception{}   
}

4. 构造器不遵循上述规则，因为构造器不遵循JAVA的覆盖和重载规则。

class TestA {
	public TestA() throws IOException {}

	public TestA(int i) {}
}

class TestC extends TestA {
	// compiles fine if current constructor doesnt throw anything.
	public TestC() { super(0); }
}

class TestB extends TestA {
	// compiles fine even if current constructor throws exceptions which dont
	// inherit from exceptions that are thrown by the overrided method of the
	// base class
	// this also means constructors dont conform the inheriting system of JAVA
	// class
	public TestB() throws Exception {}
}

5. 当一个类继承某个类，以及实现若干个接口，而被继承的类与被实现的接口拥有共同的方法，并且该方法被覆盖时，它所声明抛出的异常必须与它父类以及接口一致。

class ExceptionA extends Exception{
}
class ExceptionB extends Exception{
	
}
interface TestA{
	void method() throws ExceptionA;
}
abstract class TestB{
	abstract void method() throws ExceptionB;
}
class TestC extends TestB implements TestA{
	//compiles error
	public void method() throws ExceptionA{}
}
class TestD extends TestB implements TestA{
	//compiles error
	public void method() throws ExceptionB{}
}
class TestE extends TestB implements TestA{
	//compiles error
	public void method() throws ExceptionA,ExceptionB{}
}
class TestF extends TestB implements TestA{
	//compiles fine
	public void method(){}
}