java - Why do we use Constants? -

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why use constants , initialize them in code?i don't why use them. example here:

  public class utils {       public static final string base_url =      "api.openweathermap.org/data/2.5/weather?q=";      public static final string icon_url =      "api.openweathermap.org/data/2.5/weather?q="; }

constant use maintain , manage constant value in 1 place. example, if going hit server url multiple time can avoid multiple time declare same url. need set delay runnable on time can create constant value (i.e public static final integer delay = 5000; ). use runnable. see below example.

private static final integer delay_time = 3000; private handler mhanlder = new handler();  mhanlder.postdelayed(manimrunnable, delay_time)// same delay using 1 constant variable. mhanlder.postdelayed(mtextupdaterunnable, delay_time)// same delay using 1 constant variable.  private runnable manimrunnable = new runnable() {         public void run() {          //your animation task           }     };      private runnable mtextupdaterunnable = new runnable() {         public void run() {          //your text update task           }     };

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