InstantiationException Exception

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    InstantiationException Exception：当程序试图使用Class类中的newInstance方法创建一个类的实例，而指定的类对象因为是一个接口或是一个抽象类而无法实例化时，抛出该异常。

我们在使用newInstance()实例化对象时，程序经常会抛出InstantiationException Exception，其原因为：

newInstance: 弱类型。低效率。只能调用无参构造。即如果你重写了类的构造函数的话，一定要重写不带参数的构造函数
new: 强类型。相对高效。能调用任何public构造。
newInstance()是实现IOC、反射、依赖倒置 等技术方法的必然选择，new 只能实现具体类的实例化，不适合于接口编程。类里面就是通过这个类的默认构造函数构建了一个对象，如果没有默认构造函数就抛出InstantiationException, 如果没有访问默认构造函数的权限就抛出IllegalAccessException

abstract class Operation {
	private double num1;
	private double num2;
	public double getNum1() {
		return num1;
	}
	public void setNum1(double num1) {
		this.num1 = num1;
	}
	public double getNum2() {
		return num2;
	}
	public void setNum2(double num2) {
		this.num2 = num2;
	}	
	public double getResult() {
		double result = 0;
		return result;
	}
}

class OperationAdd extends Operation{
	public double getResult() {
		double result = 0;
		return result = getNum1() + getNum2();
	}
}
class OperationSub extends Operation {
	public double getResult() {
		double result = 0;
		return result = getNum1() - getNum2();
	}
}
class OperationMul extends Operation {
	public double getResult() {
		double result = 0;
		return result = getNum1() * getNum2();
	}
}
class OperationDiv extends Operation {
	public double getResult() {
		double result = 0;
		return result = getNum1() / getNum2();
	}
}
class OperationFactory {
	public static Operation createOperate(String operate) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
		Operation oper = null;
		switch (operate) {
		case "+" :
			oper = (OperationAdd.class.newInstance());
			break;
		case "-" :
			oper = (OperationSub.class.newInstance());
			break;
		case "*" :
			oper = (OperationMul.class.newInstance());
			break;
		case "/" :
			oper = (OperationDiv.class.newInstance());
			break;
		}
		return oper;
	}
}
/*class OperationFactory {
	public static Operation createOperate(String operate) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
		Operation oper = null;
		switch (operate) {
		case "+" :
			oper = new OperationAdd();
			break;
		case "-" :
			oper = new OperationSub();
			break;
		case "*" :
			oper = new OperationMul();
			break;
		case "/" :
			oper = new OperationDiv();
			break;
		}
		return oper;
	}
}*/
public class Calculator  {
	public static void main(String[] args) throws InstantiationException, IllegalAccessException, ClassNotFoundException{
		Operation oper = OperationFactory.createOperate("/");
		oper.setNum1(1);
		oper.setNum2(2);
		System.out.println(oper.getResult());
		
	}
	
	
	
}