Lernen Enums with Methods | Advanced Enum Features

In Java, enums are more than just collections of constants—they can also contain methods, fields, and even abstract methods that each constant must implement. By adding methods to an enum, you can give each constant its own behavior, making your code more flexible and easier to maintain. One powerful technique is using constant-specific class bodies, which allow you to override methods for individual constants, much like subclassing. This is especially useful when you want each enum constant to behave differently for a shared operation.

Operation.java


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package com.example;

public enum Operation {
    PLUS {
        @Override
        public double apply(double x, double y) {
            return x + y;
        }
    },
    MINUS {
        @Override
        public double apply(double x, double y) {
            return x - y;
        }
    },
    TIMES {
        @Override
        public double apply(double x, double y) {
            return x * y;
        }
    },
    DIVIDE {
        @Override
        public double apply(double x, double y) {
            return x / y;
        }
    };

    public abstract double apply(double x, double y);
}

By using constant-specific class bodies, you can give each enum constant its own implementation of a method. This approach is closely related to the strategy pattern in object-oriented design, where you define a family of algorithms, encapsulate each one, and make them interchangeable. With enums, you can bundle related behaviors directly with the constants, reducing the need for external classes or switch statements and making your code more concise and expressive.

EnumMethodDemo.java


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package com.example;

public class Main {
    public static void main(String[] args) {
        double x = 10.0;
        double y = 5.0;
        for (Operation op : Operation.values()) {
            System.out.println(op + ": " + op.apply(x, y));
        }
    }
}

enum Operation {
    PLUS {
        @Override
        public double apply(double x, double y) {
            return x + y;
        }
    },
    MINUS {
        @Override
        public double apply(double x, double y) {
            return x - y;
        }
    },
    TIMES {
        @Override
        public double apply(double x, double y) {
            return x * y;
        }
    },
    DIVIDE {
        @Override
        public double apply(double x, double y) {
            return x / y;
        }
    };

    abstract double apply(double x, double y);
}

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Abschnitt 2. Kapitel 2

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Operation.java


              12345678910111213141516171819202122232425262728293031
            
package com.example;

public enum Operation {
    PLUS {
        @Override
        public double apply(double x, double y) {
            return x + y;
        }
    },
    MINUS {
        @Override
        public double apply(double x, double y) {
            return x - y;
        }
    },
    TIMES {
        @Override
        public double apply(double x, double y) {
            return x * y;
        }
    },
    DIVIDE {
        @Override
        public double apply(double x, double y) {
            return x / y;
        }
    };

    public abstract double apply(double x, double y);
}

EnumMethodDemo.java


              12345678910111213141516171819202122232425262728293031323334353637383940
            
package com.example;

public class Main {
    public static void main(String[] args) {
        double x = 10.0;
        double y = 5.0;
        for (Operation op : Operation.values()) {
            System.out.println(op + ": " + op.apply(x, y));
        }
    }
}

enum Operation {
    PLUS {
        @Override
        public double apply(double x, double y) {
            return x + y;
        }
    },
    MINUS {
        @Override
        public double apply(double x, double y) {
            return x - y;
        }
    },
    TIMES {
        @Override
        public double apply(double x, double y) {
            return x * y;
        }
    },
    DIVIDE {
        @Override
        public double apply(double x, double y) {
            return x / y;
        }
    };

    abstract double apply(double x, double y);
}

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 2

Enums with Methods

1. What is a constant-specific class body in an enum?

2. Can enums have abstract methods?

3. When would you use methods inside an enum?

Enums with Methods

1. What is a constant-specific class body in an enum?

2. Can enums have abstract methods?

3. When would you use methods inside an enum?