Kotlin Builder

ExtensionFunctionJavaBytecode.java

public static final void printText(@NotNull SimpleClass $this$printText) {
   Intrinsics.checkNotNullParameter($this$printText, "$this$printText");
   String var1 = $this$printText.getText();
   System.out.println(var1);
}

KotlinClassWithBuilder.kt

class SimpleClass private constructor(val text: String?, val count: Int) {

    class Builder(var text: String? = null, var count: Int? = null) {

        fun build() = SimpleClass(text = text, count = count)

    }

}

fun SimpleClass.printText() {
    println(text)
}

fun main() {
    val simpleClass = SimpleClass.Builder().build()
    simpleClass.printText()
}

LambdaWithReceiver.kt

fun buildSimpleClass(
    configure: SimpleClass.Builder.() -> Unit
): SimpleClass {
    val builder = SimpleClass.Builder()
    builder.configure()
    return builder.build()
}

SimpleClass.java

public class SimpleClass {

    public final String text;
    public final int count;

    private SimpleClass(String text, int count) {
        this.text = text;
        this.count = count;
    }

    public static class Builder {

        private String text;
        private int count;

        public Builder setText(String text) {
            this.text = text;
            return this;
        }

        public Builder setCount(int count) {
            this.count = count;
            return this;
        }

    }

}

UseJavaBuilder.java

SimpleClass.Builder builder = new SimpleClass.Builder();
builder.setCount(1).setText("Some text");
SimpleClass result = builder.build();

UsingLambdaWithReceiver.kt

val simpleClass = buildSimpleClass { 
    text = "Some text"
    count = 4
}

simpleClass.printText() // Will print “Some text”