(求助) 2 classes - JAVA论坛

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(求助) 2 classes

(1) The Policy Class

Define a public class called Policy which has a private static/class variable
called NEXT_POLICY_NUMBER which is an int (initially set to 1) representing
the number to be given to the next policy created. Create the following attributes
in the class as well:

• a private attribute called policyNumber of type int that identifies the policy with a unique integer.
• a protected attribute called amount that contains the amount (a float) of coverage for the policy.

Create a public constructor which takes a single float parameter and uses it to set the amount variable. The constructor sets the policyNumber such that each created policy has a unique number and also updates the class variable appropriately.

Create public get methods for your attributes as well as a public toString() method that returns a String with the following format (use String.format() for both the policy number and amount):
Policy: 0001 amount: $320.00

Create a public instance method called isExpired() which always returns false. Now test your code with this program:

程序代码：

public class PolicyTestProgram {
    public static void main(String args[]) {
          System.out.println(new Policy(320)); // displays Policy: 0001 amount: $320.00
          System.out.println(new Policy(500.1f)); // displays Policy: 0002 amount: $500.10
          System.out.println(new Policy(0)); // displays Policy: 0003 amount: $0.00
          System.out.println(new Policy(320).isExpired()); // displays false
     }
}

(2) The DepreciablePolicy Class
Now we will make some subclasses to represent different types of policies. Define a
public class called DepreciablePolicy as a subclass of Policy which has a private
attribute called rate of type float which represents the rate at which the policy
depreciates each time a claim is made. For example, a rate of 0.10 means that the
value of the policy (i.e., the amount) depreciates 10% each time a claim is made (we
will discuss the making of claims in the next section). Implement these:

• a public constructor which takes a float representing the amount and another float representing
the rate. This constructor should use inheritance by calling the constructor from the superclass to
set the amount and policyNumber.

• a public get method for the rate.

• a public toString() method that returns a String with the following format:

DepreciablePolicy: 0001 amount: $320.00 rate: 10.0%

You MUST make use of inheritance by calling the toString() from the superclass (You will have to
make a change to the Policy class’ toString() method as well. Also, use String.format() again to
display the rate.

• an instance method called isExpired() which returns true if the amount of this policy has
depreciated to 0. You should be able to write this method WITHOUT any IF statements … try.

• an instance method called depreciate() which reduces the amount of the policy by the rate
percentage. For example, if the amount is $100 and the rate is 0.10, then the amount after this
method is called once should be $90.

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public class Policy { private static int NEXT_POLICY_NUMBER = 1; private int policyNumber; protected float amount; //Constructors public Policy(float a) { this.policyNumber = 0; this.amount = a; this.policyNumber = NEXT_POLICY_NUMBER; NEXT_POLICY_NUMBER++; } //Get method public int getPolicyNumber() { return this.policyNumber; } public float getAmount() { return this.amount; } //Set method public void setPolicyNumber(int newPolicyNumber) { this.policyNumber = newPolicyNumber; } public void setAmount(float a) { this.amount = a; } //toString Method public String toString() { return ("Policy:" + String.format("%,04i", this.policyNumber) + "amount:" + "$" + String.format ("%,3.2f", this.amount)); } public boolean isExpired(){ return false; }