sakata1222/expressionj

ExpressionJ

Java library for supporting the following expressions:

• If expression

Java versions:

• 8 or later

If expression

"FizzBuzz" can be implemented as following:

import static jp.gr.java_conf.spica.expressionj.Expressions.ifExp;

/*..snip..*/

String fizzBuzz = ifExp(i % 15 == 0).then(() -> "FizzBuzz")
    .elseIf(() -> i % 3 == 0).then(() -> "Fizz")
    .elseIf(() -> i % 5 == 0).then(() -> "Buzz")
    .elseExp(() -> String.valueOf(i));

Switch expression

If you use Java14 or later, you can use the official switch expression .

import static jp.gr.java_conf.spica.expressionj.Expressions.switchExp;
import static jp.gr.java_conf.spica.expressionj.switchexpression.Cases.caseEq;
import static jp.gr.java_conf.spica.expressionj.switchexpression.Cases.caseIn;

import jp.gr.java_conf.spica.expressionj.switchexpression.Cases;

/*..snip..*/

int length = switchExp(day).cases(
    caseIn(MONDAY, FRIDAY, SUNDAY).yield(() -> 6),
    caseEq(TUESDAY).yield(() -> 7),
    caseIn(THURSDAY, SATURDAY).yield(() -> 8),
    caseIn(WEDNESDAY).yield(() -> 9),
    Cases.<Day>caseDefault().yield(() -> -1));

import static jp.gr.java_conf.spica.expressionj.Expressions.switchExp;

import jp.gr.java_conf.spica.expressionj.switchexpression.Cases;

/*..snip..*/

double perimeter = switchExp(shape).cases(
    Cases.<Shape, Rectangle>caseInstanceOf(Rectangle.class)
        .yield(r -> r.length * 2 + r.width * 2),
    Cases.<Shape, Circle>caseInstanceOf(Circle.class)
        .yield(r -> 2 * r.radius * Math.PI));

Sample code

See also the sample code

Performance

If expression

If expression is a little slower than If statement, but it's enough fast when number of calls is not huge (e.g. over 10000000(10^7)).

Here is a result of the benchmark in the CI environment.

The benchmark just performs solve FizzBuzz and sum up of the length of the result.

• java.vm.vendor:AdoptOpenJDK
• java.vm.version:11.0.11+9
• os.name:Linux
• os.version:5.13.0-1023-azure

Benchmark of FizzBuzz.

Loop count is 10000000.

Elapsed Time in ms:

Count	If statement with method	If Expression
1	252	880
2	266	585
3	270	582
4	270	581
5	265	594
6	269	580

Switch expression

Switch expression is slower than Switch statement, and might be slower than official switch expression. When the number of calls is little huge (e.g. over 1000000(10^6)), please use switch statement or official switch expression.

Here is a result of the benchmark in the CI environment.

• java.vm.vendor:AdoptOpenJDK
• java.vm.version:11.0.11+9
• os.name:Linux
• os.version:5.13.0-1023-azure

Benchmark of length count of days. Loop count is 125000. Elapsed Time in ms:

Count	Switch statement with method	Switch Expression
1	95	747
2	51	525
3	51	481
4	28	477
5	20	478
6	20	476

Changelog

See CHANGELOG.md