Los operadores de igualdad y relacionales
Los operadores de igualdad y relacionales determinan si un operando es mayor, menor, igual a o distinto de otro. Probablemente la mayoría de estos operadores también le serán familiares. Tenga en mente que debe utilizar «==», no «=» cuando compruebe si dos valores primitivos son iguales.
== igual a
!= distinto de
> mayor que
>= mayor que o igual a
< menor que
<= menor que o igual a
El siguiente programa, ComparisonDemo, comprueba los operadores de comparación:
/*
* 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 ComparisonDemo {
public static void main(String[] args){
int value1 = 1;
int value2 = 2;
if(value1 == value2) System.out.println("value1 == value2");
if(value1 != value2) System.out.println("value1 != value2");
if(value1 > value2) System.out.println("value1 > value2");
if(value1 < value2) System.out.println("value1 < value2");
if(value1 <= value2) System.out.println("value1 <= value2");
}
}
Resultado:
value1 != value2
value1 < value2
value1 <= value2
Los operadores condicionales
Los operadores && y || realizan las operaciones AND-Condicional y OR-Condicional sobre dos expresiones booleanas. Estos operadores muestran un comportamiento de «cortocircuito», lo que significa que el segundo operando solamente se evalúa si es necesario.
&& AND-Condicional
|| OR-Condicional
El siguiente programa, ConditionalDemo1, comprueba estos operadores:
/*
* 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 ConditionalDemo1 {
public static void main(String[] args){
int value1 = 1;
int value2 = 2;
if((value1 == 1) && (value2 == 2)) System.out.println("value1 es 1 Y value2 es 2");
if((value1 == 1) || (value2 == 1)) System.out.println("value1 es 1 O value2 es 1");
}
}
Otro de los operadores condicionales es ?:, que se puede considerar una abreviatura de una sentencia if-then-else (tratada en la sección Sentencias de control de flujo de esta lección). Este operador también se conoce como el operador ternario porque utiliza tres operandos. En esl siguiente ejemplo este operador se debe leer como: «Si unaCondicion es true (verdadera), asigna el valor de valor1 a resultado. Si no, asigna el valor de valor2 a resultado.»
El siguiente programa, ConditionalDemo2, comprueba el operador ?: :
/*
* 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 ConditionalDemo2 {
public static void main(String[] args){
int valor1 = 1;
int valor2 = 2;
int resultado;
boolean unaCondicion = true; // es verdadera
resultado = unaCondicion ? valor1 : valor2;
System.out.println(resultado);
}
}
Puesto que unaCondicion es true (verdadera), este programa imprime «1» en la pantalla. Utilice el operador ?: en lugar de una sentencia if-then-else si hace que su código sea más legible, por ejemplo cuando las expresiones con compactas y no tienen efectos secundarios (como asignaciones).
El operador de comparación de tipos «instanceof»
El operador instanceof compara un objeto con un tipo indicado. Puede utilizarlo para comprobar si un objeto es una instancia de una clase, una instancia de una subclase o una instancia de una clase que implementa una interfaz en concreto.
El siguiente programa, InstanceofDemo, define una clase padre (llamada Parent), una interfaz sencilla (llamada MyInterface), y una clase hija (llamada Child) que hereda del padre e implementa la interfaz.
/*
* 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 InstanceofDemo {
public static void main(String[] args) {
Parent obj1 = new Parent();
Parent obj2 = new Child();
System.out.println("obj1 instanceof Parent: " + (obj1 instanceof Parent));
System.out.println("obj1 instanceof Child: " + (obj1 instanceof Child));
System.out.println("obj1 instanceof MyInterface: " + (obj1 instanceof MyInterface));
System.out.println("obj2 instanceof Parent: " + (obj2 instanceof Parent));
System.out.println("obj2 instanceof Child: " + (obj2 instanceof Child));
System.out.println("obj2 instanceof MyInterface: " + (obj2 instanceof MyInterface));
}
}
class Parent{}
class Child extends Parent implements MyInterface{}
interface MyInterface{}
Resultado:
obj1 instanceof Parent: true
obj1 instanceof Child: false
obj1 instanceof MyInterface: false
obj2 instanceof Parent: true
obj2 instanceof Child: true
obj2 instanceof MyInterface: true
Al usar el operador instanceof, tenga en cuenta que null no es una instancia de nada.
