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Diffstat (limited to 'java.html.markdown')
| -rw-r--r-- | java.html.markdown | 66 |
1 files changed, 62 insertions, 4 deletions
diff --git a/java.html.markdown b/java.html.markdown index aae64ccf..1813f81c 100644 --- a/java.html.markdown +++ b/java.html.markdown @@ -186,9 +186,9 @@ public class LearnJava { // operations perform as could be expected for a // doubly-linked list. // Maps - A set of objects that map keys to values. Map is - // an interface and therefore cannot be instantiated. - // The type of keys and values contained in a Map must - // be specified upon instantiation of the implementing + // an interface and therefore cannot be instantiated. + // The type of keys and values contained in a Map must + // be specified upon instantiation of the implementing // class. Each key may map to only one corresponding value, // and each key may appear only once (no duplicates). // HashMaps - This class uses a hashtable to implement the Map @@ -697,6 +697,64 @@ public abstract class Mammal() return true; } } + + +// Enum Type +// +// An enum type is a special data type that enables for a variable to be a set of predefined constants. The // variable must be equal to one of the values that have been predefined for it. +// Because they are constants, the names of an enum type's fields are in uppercase letters. +// In the Java programming language, you define an enum type by using the enum keyword. For example, you would +// specify a days-of-the-week enum type as: + +public enum Day { + SUNDAY, MONDAY, TUESDAY, WEDNESDAY, + THURSDAY, FRIDAY, SATURDAY +} + +// We can use our enum Day like that: + +public class EnumTest { + + // Variable Enum + Day day; + + public EnumTest(Day day) { + this.day = day; + } + + public void tellItLikeItIs() { + switch (day) { + case MONDAY: + System.out.println("Mondays are bad."); + break; + + case FRIDAY: + System.out.println("Fridays are better."); + break; + + case SATURDAY: + case SUNDAY: + System.out.println("Weekends are best."); + break; + + default: + System.out.println("Midweek days are so-so."); + break; + } + } + + public static void main(String[] args) { + EnumTest firstDay = new EnumTest(Day.MONDAY); + firstDay.tellItLikeItIs(); // => Mondays are bad. + EnumTest thirdDay = new EnumTest(Day.WEDNESDAY); + thirdDay.tellItLikeItIs(); // => Midweek days are so-so. + } +} + +// Enum types are much more powerful than we show above. +// The enum body can include methods and other fields. +// You can se more at https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html + ``` ## Further Reading @@ -720,7 +778,7 @@ The links provided here below are just to get an understanding of the topic, fee * [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html) -* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconv-138413.html) +* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconvtoc-136057.html) **Online Practice and Tutorials** |