{"id":639,"date":"2018-01-19T07:00:26","date_gmt":"2018-01-19T07:00:26","guid":{"rendered":"https:\/\/manualjavaoracle.wordpress.com\/?p=639"},"modified":"2018-02-09T13:29:51","modified_gmt":"2018-02-09T18:29:51","slug":"constantes","status":"publish","type":"post","link":"https:\/\/www.manualjava.net\/?p=639","title":{"rendered":"Constantes"},"content":{"rendered":"<p><img decoding=\"async\" loading=\"lazy\" class=\" wp-image-1235 alignnone\" src=\"https:\/\/www.manualjava.net\/wp-content\/uploads\/2018\/01\/java41.png\" alt=\"\" width=\"264\" height=\"156\" \/><\/p>\n<p><span style=\"color: #000000;\">En numerosos programas se necesitan constantes num\u00e9ricas pero es una buena idea usar nombres simb\u00f3licos para todos los valores, incluso para los que parecen evidentes. En Java, las constantes se identifican con la palabra clave <strong>final<\/strong>. Una variable etiquetada como final nunca puede modificar su valor ya que se ha convertido en una constante.<\/span><!--more--><\/p>\n<h3><strong><span style=\"color: #000000;\">Regla<\/span><\/strong><\/h3>\n<p style=\"text-align: left;\"><span style=\"color: #000000;\">Utilizar constantes con nombres para hacer sus programas m\u00e1s f\u00e1ciles de leer y mantener.<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">Muchos programadores utilizan nombres en letras may\u00fasculas para constantes (variables final).<\/span><\/li>\n<\/ul>\n<h3><span style=\"color: #000000;\">\u00a0<\/span><strong><span style=\"color: #000000;\">Ejemplo<\/span><\/strong><\/h3>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0final double VALOR_DESCUENTO = 14.50;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0final double IVA = 16;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0final double EURO = 166.67;<\/span><\/p>\n<p><span style=\"color: #000000;\">A veces se necesitan valores constantes en diferentes m\u00e9todos de una clase. Entonces deben declararse junto con los campos instancia de una clase y etiquetarse como\u00a0<strong>static y final.\u00a0<\/strong>La palabra reservada static significa que la constante pertenece a la clase.<\/span><\/p>\n<h3><strong><span style=\"color: #000000;\">Ejemplo<\/span><\/strong><\/h3>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 public class MercadoValores <\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 { <\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\/\/ m\u00e9todos<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 . . .<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\/\/ constantes<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0public static final double PESO = 0.55;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0public static final double EURO = 1.55;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 }<\/span><\/p>\n<h2><strong><span style=\"color: #000000;\">Definici\u00f3n de constantes en un m\u00e9todo o en una clase<\/span><\/strong><\/h2>\n<ol>\n<li><span style=\"color: #000000;\">En un m\u00e9todo<\/span><\/li>\n<\/ol>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 final Tipo nombreVariable = expresi\u00f3n;<\/span><\/p>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 2. En una clase<\/span><\/p>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 especificadorAcceso static final Tipo nombreVariable = expresi\u00f3n;<\/span><\/p>\n<h3><strong><span style=\"color: #000000;\">Ejemplo<\/span><\/strong><\/h3>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 final double VALOR_EURO = 166.67;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 public static final double EUROS_LITRO = 1.75;<\/span><\/p>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0Una clase Constantes para representar formatos de impresion.<\/span><\/p>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0public class Constantes<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0{<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0public static void main(String [] args)<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0{<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0final int NUMERO_LINEAS_PAGINA = 55;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0final double ANCHURA_PAPEL = 20.5;<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0System.out.println(\u00abTama\u00f1o papel: \u00bb +<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 ANCHURA_PAPEL * NUMERO_LINEAS_PAGINA);<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0}<\/span><br \/>\n<span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0}<\/span><\/p>\n<p><span style=\"color: #000000;\">Las clases en Java permiten declarar constantes que estar\u00e1n disponibles para todos los m\u00e9todos de la clase, incluso para otras clases. Estas constantes se denominan\u00a0<strong>constantes de clases.\u00a0<\/strong>Se establece una constante de clase con las palabras reservadas\u00a0<strong>static final.\u00a0<\/strong>Un ejemplo de uso de una constante de clase:<\/span><\/p>\n<p><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 public class ConstantesDemo<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 {<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 public static void main(String [] args)<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 {<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0double anchoPapel = 24.5;<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0double altoPapel = 54.5;<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0. . .<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 }<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 public static final double IVA = 20;<\/span><br \/>\n<span style=\"color: #000000;\"> \u00a0 \u00a0 \u00a0 }<\/span><\/p>\n<p><span style=\"color: #000000;\">Obs\u00e9rvese que la definici\u00f3n de la constante de clase aparece fuera del m\u00e9todo main. Por consiguiente la constante puede ser utilizada en otros m\u00e9todos de la misma clase.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>En numerosos programas se necesitan constantes num\u00e9ricas pero es una buena idea usar nombres simb\u00f3licos para todos los valores, incluso para los que parecen evidentes. En Java, las constantes se identifican con la palabra clave final. Una variable etiquetada como final nunca puede modificar su valor ya que se ha convertido en una constante.<\/p><p><a class=\"more-link btn\" href=\"https:\/\/www.manualjava.net\/?p=639\">Seguir leyendo<\/a><\/p>\n","protected":false},"author":1,"featured_media":1235,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"_links":{"self":[{"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/posts\/639"}],"collection":[{"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=639"}],"version-history":[{"count":1,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/posts\/639\/revisions"}],"predecessor-version":[{"id":2090,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/posts\/639\/revisions\/2090"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=\/wp\/v2\/media\/1235"}],"wp:attachment":[{"href":"https:\/\/www.manualjava.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=639"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=639"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.manualjava.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=639"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}