Better Strings - Java String Interpolation

The Java Plugin to use string interpolation for Java (like in Kotlin). Supports Java 8, 9, 10, 11, …​

1. Motivation

In the latest JEPs https://openjdk.java.net/jeps/355, we have the only expectation of the RAW string literals, but there is nothing about the string interpolation.

And it’s so sad, that we need writing code like this in the 2020 year:

int a = 3;
int b = 4;
System.out.println(a + " + " + b + " = " + (a + b));

just to print the string: 3 + 4 = 7

of course, we can use a var since Java 10:

var a = 3;
var b = 4;
System.out.println(a + " + " + b + " = " + (a + b));

But this code is still sad =(

2. What can we do with the Better Strings plugin?

2.1. Using variables in string literals:

var a = 3;
var b = 4;
System.out.println("${a} + ${b} = ${a+b}");

prints: 3 + 4 = 7

2.2. Using expressions:

var a = 3;
var b = 4;
System.out.println("flag = ${a > b ? true : false}");

prints: flag = false

var a = 3;
System.out.println("pow = ${a * a}");

prints: pow = 9

2.3. Using functions:

@Test
void functionCall() {
    System.out.println("fact(5) = ${factorial(5)}");
}

long factorial(int n) {
    long fact = 1;
    for (int i = 2; i <= n; i++) {
        fact = fact * i;
    }
    return fact;
}

prints: fact(5) = 120

3. Getting started

You need to add the following dependency:

<dependency>
    <groupId>com.antkorwin</groupId>
    <artifactId>better-strings</artifactId>
    <version>0.3</version>
</dependency>

And you can use string interpolation anywhere in your code.

4. How to turn-off string interpolation

To skip the string interpolation for class, method or field you can use the @DisabledStringInterpolation annotation:

@DisabledStringInterpolation
class Foo {
    void test() {
        System.out.println("${a+b}");
    }
}

this code prints: ${a+b}

Also, you can use the following workaround to escape string interpolation locally in your code:

System.out.println("${'$'}{a+b}");

the result is : ${a+b}

5. How it works

Better Strings is a Java Annotation Processor, but it does not process specific annotations, it makes AST modification of your code while javac compiling it.

Note	Keep in mind that this feature should be used carefully. You shouldn’t write too much code inside string literals because it is too difficult to maintain and maybe not obvious for debugging.

6. How to use with other annotation processors

If you need to use multiple annotation processors (for example better-strings with lombok or mapstruct) and the order of processing is necessary for you then you can set the order in your building tool.

In maven, you should declare dependencies as usually, then describe annotation processors in the configuration of the maven-compiler-plugin in the build section:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.5.1</version>
    <configuration>
        <annotationProcessorPaths>

            <!-- first annotation processor -->
            <path>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <version>${lombok.version}</version>
            </path>

            <!-- second annotation processor -->
            <path>
               <groupId>com.antkorwin</groupId>
               <artifactId>better-strings</artifactId>
               <version>${better-strings.version}</version>
            </path>

        </annotationProcessorPaths>
    </configuration>
</plugin>

Note	The order of annotation processors paths is necessary. You should describe the all used APT when you write annotationProcessorPaths section.