Java Program - Action Event. Need Help ...

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Câu 1: chọn "lớp con có thể khai báo biến chưa có trên lớp cha".
Câu 2: viết thử 1 chương trình có biến mang thuộc tính private static rồi thử xem cái nào lỗi.

Mã:

package untitled1;

class Assembly {
  /* Instance Variables */
  private String name;
  private Date today;
  private int discount;
//define instance variables named parta, partb, partc
  private Part part1;
  private Part part2;
  private Part part3;

  public Assembly(String assemblyName,
                  int m, int d, int y,
                  int percentage,
                  Part partA , Part partB , Part partC ) {
    name = assemblyName;
    today = new Date(m, d, y);
    discount = percentage;
    part1 = partA;
    part2 = partB;
    part3 = partC;
  }

  public int price() {
    /*Return my total un-discounted price in dollars.*/
    return part1.price() + part2.price() + part3.price();
  }

  public int discountedPrice() {
    /*Return my discounted price in dollars.*/
    double price;
    price = price() * (1 - discount);
    return (int)(price);
  }

  public void display() {
    System.out.println(name); //display name
    System.out.print("\tAssembled on");
    System.out.println(today); //display date
    System.out.println("\tConsists of");
    System.out.print("\t");
    this.part1.display();
    System.out.print("\t");
    this.part2.display();
    System.out.print("\t");
    this.part3.display();
    System.out.print("\tTotal $");
    System.out.println(price()); //display price
    System.out.print("Discount ");
    System.out.print(discount); //display discount
    System.out.println("%");
    System.out.print("Discounted price $");
    System.out.println(discountedPrice()); //display discounted price
  }

}

class Part {
  private String name;
  private int price;

  public Part(String partName, int value) {
    name = partName;
    price = value;
  }

  public void display() {
    /*Display part name*/
    System.out.print(name);

    System.out.print(" $");

    /*Display part price*/
    System.out.println(price);
  }

  public int price() {
    return price;
  }
}

class Date {
  private int month; // 1-12
  private int day; // 1-31 based on month
  private int year; // any year
  //Constructor
  public Date(int mn, int dy, int yr) {
    month = mn;
    day = dy;
    year = yr;
  }

  // Create a String of the form month/day/year
  public String toString() {
    return month + "/" + day + "/" + year;
  }
}

class Test {

  //Test the Assembly and Parts classes by creating an assembly and displaying it.

  public static void main(String args[]) {
  /*Create the 3 part objects part1, part2, part3, create the an assembly object that contains them and
  display the assembly. */
//Create object part1 with the values "Engine", 6000
    Part partA = new Part("Engine", 6000);
//(Create object part2 with the values"Frame", 7000;
    Part partB = new Part("Frame", 7000);
//Create object part3 with the values"Interior", 4000;
    Part partC = new Part("Interior", 4000);
//Create object assembly with the values"Automobile", 12,1,2006, 10, part1, part2, part3;
    Assembly assembly = new Assembly("Automobile", 12, 1, 2006, 10, partA, partB, partC);
    assembly.display();
  }
}

Lớp lưu trữ các thông tin của sự kiện action.

http://java.sun.com/docs/books/tutorial/java/javaOO/thiskey.html

You can declare a variable in any scope to be final. The value of a final variable cannot change after it has been initialized. Such variables are similar to constants in other programming languages.
To declare a final variable, use the final keyword in the variable declaration before the type.

final int aFinalVar = 0;

The previous statement declares a final variable and initializes it all at once. Subsequent attempts to assign a value to aFinalVar result in a compiler error. You may, if necessary, defer initialization of a final local variable. Simply declare the local variable and initialize it later, as follows.
final int blankfinal;
. . .
blankfinal = 0;

A final local variable that has been declared but not yet initialized is called a blank final. Again, once a final local variable has been initialized, it cannot be set, and any later attempts to assign a value to blankfinal result in a compile-time error.