Java Language Enums Enum constant specific body
Example
In an enum it is possible to define a specific behavior for a particular constant of the enum which overrides the default behavior of the enum, this technique is known as constant specific body.
Suppose three piano students - John, Ben and Luke - are defined in an enum named PianoClass, as follows:
enum PianoClass {
JOHN, BEN, LUKE;
public String getSex() {
return "Male";
}
public String getLevel() {
return "Beginner";
}
}
And one day two other students arrive - Rita and Tom - with a sex (Female) and level (Intermediate) that do not match the previous ones:
enum PianoClass2 {
JOHN, BEN, LUKE, RITA, TOM;
public String getSex() {
return "Male"; // issue, Rita is a female
}
public String getLevel() {
return "Beginner"; // issue, Tom is an intermediate student
}
}
so that simply adding the new students to the constant declaration, as follows, is not correct:
PianoClass2 tom = PianoClass2.TOM;
PianoClass2 rita = PianoClass2.RITA;
System.out.println(tom.getLevel()); // prints Beginner -> wrong Tom's not a beginner
System.out.println(rita.getSex()); // prints Male -> wrong Rita's not a male
It's possible to define a specific behavior for each of the constant, Rita and Tom, which overrides the PianoClass2 default behavior as follows:
enum PianoClass3 {
JOHN, BEN, LUKE,
RITA {
@Override
public String getSex() {
return "Female";
}
},
TOM {
@Override
public String getLevel() {
return "Intermediate";
}
};
public String getSex() {
return "Male";
}
public String getLevel() {
return "Beginner";
}
}
and now Tom's level and Rita's sex are as they should be:
PianoClass3 tom = PianoClass3.TOM;
PianoClass3 rita = PianoClass3.RITA;
System.out.println(tom.getLevel()); // prints Intermediate
System.out.println(rita.getSex()); // prints Female
Another way to define content specific body is by using constructor, for instance:
enum Friend {
MAT("Male"),
JOHN("Male"),
JANE("Female");
private String gender;
Friend(String gender) {
this.gender = gender;
}
public String getGender() {
return this.gender;
}
}
and usage:
Friend mat = Friend.MAT;
Friend john = Friend.JOHN;
Friend jane = Friend.JANE;
System.out.println(mat.getGender()); // Male
System.out.println(john.getGender()); // Male
System.out.println(jane.getGender()); // Female
