1.1. Файл CalcModel.Java

package com.devious.calculator;

import java.util.Observable;

/**

* The CalcModel class serves as the "mechanics" behind our

* calculator. It handles "presses" of the calculators "buttons",

* performs calculators, and keeps the "display" up-to-date.

* The CalcModel extends Observable and will notify subscribers

* whenever the calculators display should change.

*

*/

public class CalcModel extends Observable

{

/**

* No operation in progress

*/

public static final int OP_NONE = 0;

/**

* Addition operation

*/

public static final int OP_ADD = 1;

/**

* Subtration operation

*/

public static final int OP_SUB = 2;

/**

* Multiplication operation

*/

public static final int OP_MUL = 3;

/**

* Dividion operation

*/

public static final int OP_DIV = 4;

//-------------------------------------------------------------

/**

* The pendingOp represents the operation that the user

* is currently entering. Should be one of the OP_* constants

*/

private int pendingOp = 0;

/**

* The value previously entered by the user. Effectively, this

* is the number the user entered before pressing one of the

* operation (+,-,*,/) keys

*/

private int previousValue = 0;

/**

* The number the user is currently in the process of entering

*/

private int currentValue = 0;

//-------------------------------------------------------------

/**

* Returns a string representing the number the calculator

* should currently display.

*

* @return the String the calculator should display

*/

public String getValue()

{

return Integer.toString(currentValue);

}

/**

* Use this method to indicate when one of the calculator's numeric

* "keys" has been pressed.

*

* @param s a String representing the key wich was

* pressed (e.g. "0");

*/

public void addDigit(String s)

{

char c = s.charAt(0);

String val = getValue() + c;

setDisplay(Integer.parseInt(val));

}

/**

* Use this method to indicate when one of the calculator's numeric

* "keys" has been pressed.

*

* @param c a char representing the key wich was

* pressed (e.g. '0');

*/

public void addDigit(char c)

{

String val = getValue() + c;

setDisplay(Integer.parseInt(val));

}

/**

* Use this method to indicate when one of the calculator's

* operational keys have been pressed. If there is a pending

* operation, the calculation will be performed and the

* calculator's display will be updated.

*

* @param op one of the OP_* constants indicating which

* operation key was pressed

*/

public void setOperation(int op)

{

// handle case where user enters multiple operations

// without intervening '=' (e.g 1 + 1 + 1)

if (pendingOp != OP_NONE)

calculate();

previousValue = currentValue;

this.pendingOp = op;

currentValue = 0;

}

/**

* Changes the calculator's display and notifies any observers

* of the change.

*

* @param value the new value to be displayed by the calculator

*/

public void setDisplay(int value)

{

currentValue = value;

setChanged();

notifyObservers();

}

/**

* This method can be used to "clear" the calculator. Any pending

* operations and numeric entries are discarded. The calculator's

* display is updated appropriately.

*/

public void clear()

{

this.pendingOp = OP_NONE;

previousValue = 0;

setDisplay(0);

}

/**

* This method is used to process a pending calculation (e.g.

* because the equals key was pressed.

*/

public void calculate()

{

switch (pendingOp)

{

case OP_ADD:

setDisplay(previousValue + currentValue);

break;

case OP_SUB:

setDisplay(previousValue - currentValue);

break;

case OP_MUL:

setDisplay(previousValue * currentValue);

break;

case OP_DIV:

setDisplay(previousValue / currentValue);

break;

}

pendingOp = OP_NONE;

previousValue = 0;

}

}