Operadores de asignación, aritméticos y unarios (Los tutoriales Java™ > El lenguaje Java

Operadores de asignación, aritméticos y unarios

El operador de asignación sencillo

Uno de los operadores más habituales que se encontrará es el operador de asignación sencillo «=». Ya lo hemos visto en la clase Bicycle; asigna el valor a su derecha al operando a su izquierda:

int cadence = 0;
 int speed = 0;
 int gear = 1;

Este operador también se puede utilizar en objetos para asignar referencias a objetos, como se muestra en Creatción de objetos.

Los operadores aritméticos

El lenguaje de programación Java proporciona operadores que realizan la suma, resta, multiplicación y división. Probablemente los reconozca por sus homólogos en la mátemática básica. El único símbolo que le podrá parecer nuevo es «%», que divide un operando por el otro y devuelve el resto como su resultado.

+       operador de adición (también se utiliza para concatenar Strings)
-       operador de sustracción
*       operador de multiplicación
/       operador de división
%       operador de resto

El siguiente programa, ArithmeticDemo, comprueba los operadores aritméticos.

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

class ArithmeticDemo {

     public static void main (String[] args){
          
          int result = 1 + 2; // result es ahora 3
          System.out.println(result);

          result = result - 1; // result es ahora 2
          System.out.println(result);

          result = result * 2; // result es ahora 4
          System.out.println(result);

          result = result / 2; // result es ahora 2
          System.out.println(result);

          result = result + 8; // result es ahora 10
          result = result % 7; // result es ahora 3
          System.out.println(result);

     }
}

También puede combinar los operadores aritméticos con el operador de asignación sencillo para crear asignaciones compuestas. Por ejemplo, x+=1; y x=x+1; ambos incrementan el valir de x en 1.

El operador + también se puede utilizar para concatenar (unir) dos cadenas, como se muestra en el siguiente programa ConcatDemo:

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

class ConcatDemo {
     public static void main(String[] args){
          String firstString = "Esto es";
          String secondString = " una cadena concatenada.";
          String thirdString = firstString+secondString;
          System.out.println(thirdString);
     }
}

Al final de este programa la variable thirdString contiene «Esto es una cadena concatenada.», que se imprimirá en la salida estándar.

Los operadores unarios

Los operadores unarios solamente necesitan un operando; realizan diferentes operaciones como incrementar o decrementar un valor en una unidad, negar una expresión o invertir el valor de un booleano.

+       Operador unario «más», indica un valor positivo (sin embargo los número son positivos sin el operador)
-       Operador unario «menos»; niega una expresión
++      Operador de incremento; incrementa un valor en 1
--      Operador de decremento; decrementa un valor en 1
!       Operador de complemento lógico; invierte el valor de un booleano

El siguiente programa, UnaryDemo, comprueba los operadores unarios:

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

class UnaryDemo {

     public static void main(String[] args){
          int result = +1; // result es ahora 1
          System.out.println(result);
          result--;  // result es ahora 0
          System.out.println(result);
          result++; // result es ahora 1 
          System.out.println(result);
          result = -result; // result es ahora -1
          System.out.println(result);
          boolean success = false;
          System.out.println(success); // falso/false
          System.out.println(!éxito); // verdadero/true
     }
}

Los operadores de incremento y decremento se pueden aplicar delante (prefix) o detrás (postfix) del operando. Tanto el código result++; como ++result; resultarán en que result será incrementado en uno. La única diferencia es que la versión prefix (++result) evalúa según el valor incrementado, mientras que la versión postfix (result++) evalúa según el valor original. Si solamente está realizando un incremento o decremento sencillo, realmente no importa cuál de las dos formas utiliza. Pero si utiliza este operador como parte de una expresión más larga, la forma que elija puede influir significativamente en el resultado.

El siguiente programa, PrePostDemo, ilustra el operador unario de incremento prefix/postfix:

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

class PrePostDemo {
     public static void main(String[] args){
          int i = 3;
          i++;
          System.out.println(i);        // "4"
          ++i;                     
          System.out.println(i);        // "5"
          System.out.println(++i);      // "6"
          System.out.println(i++);      // "6"
          System.out.println(i);        // "7"
     }
}

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