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BAEL-9211 Introduction to the Class-File API #18517

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Merged
merged 1 commit into from
May 12, 2025
Merged

BAEL-9211 Introduction to the Class-File API #18517

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80 changes: 80 additions & 0 deletions core-java-modules/core-java-24/src/main/java/com/baeldung/classfiles/CodeGenerator.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,80 @@
package com.baeldung.classfiles;

import static java.lang.constant.ConstantDescs.CD_String;
import static java.lang.constant.ConstantDescs.CD_double;

import java.io.IOException;
import java.lang.classfile.ClassFile;
import java.lang.classfile.ClassFileBuilder;
import java.lang.classfile.ClassTransform;
import java.lang.classfile.CodeTransform;
import java.lang.classfile.Label;
import java.lang.classfile.MethodBuilder;
import java.lang.classfile.MethodTransform;
import java.lang.classfile.instruction.InvokeInstruction;
import java.lang.constant.ClassDesc;
import java.lang.constant.MethodTypeDesc;
import java.lang.reflect.AccessFlag;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.function.Consumer;

public class CodeGenerator {

public static void generate() throws IOException {

Consumer<MethodBuilder> calculateAnnualBonusBuilder = methodBuilder -> methodBuilder.withCode(codeBuilder -> {
Label notSales = codeBuilder.newLabel();
Label notEngineer = codeBuilder.newLabel();
ClassDesc stringClass = ClassDesc.of("java.lang.String");

codeBuilder.aload(3)
.ldc("sales")
.invokevirtual(stringClass, "equals", MethodTypeDesc.of(ClassDesc.of("Z"), stringClass))
.ifeq(notSales)
.dload(1)
.ldc(0.35)
.dmul()
.dreturn()
.labelBinding(notSales)
.aload(3)
.ldc("engineer")
.invokevirtual(stringClass, "equals", MethodTypeDesc.of(ClassDesc.of("Z"), stringClass))
.ifeq(notEngineer)
.dload(1)
.ldc(0.25)
.dmul()
.dreturn()
.labelBinding(notEngineer)
.dload(1)
.ldc(0.15)
.dmul()
.dreturn();
});

var classBuilder = ClassFile.of()
.build(ClassDesc.of("EmployeeSalaryCalculator"),
cb -> cb.withMethod("calculateAnnualBonus", MethodTypeDesc.of(CD_double, CD_double, CD_String), AccessFlag.PUBLIC.mask(),
calculateAnnualBonusBuilder));

Files.write(Path.of("EmployeeSalaryCalculator.class"), classBuilder);
}

public static void transform() throws IOException {
var basePath = Files.readAllBytes(Path.of("EmployeeSalaryCalculator.class"));

CodeTransform codeTransform = ClassFileBuilder::accept;

MethodTransform methodTransform = MethodTransform.transformingCode(codeTransform);
ClassTransform classTransform = ClassTransform.transformingMethods(methodTransform);

ClassFile classFile = ClassFile.of();
byte[] transformedClass = classFile.transformClass(classFile.parse(basePath), classTransform);
Files.write(Path.of("TransformedEmployeeSalaryCalculator.class"), transformedClass);
}

public static void main(String[] args) throws IOException {
generate();
transform();
}
}
10 changes: 5 additions & 5 deletions ...es/core-java-24/src/main/java/com/baeldung/javafeatures/switchpatterns/SwitchPreview.java
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
package com.baeldung.java.javafeatures;
package com.baeldung.javafeatures.switchpatterns;
import java.util.Random;

public class SwitchPreview {

void primitiveTypePatternExample() {
Random r=new Random();
switch (r.nextInt()) {
case 1 -&gt; System.out.println("int is 1");
case int i when i &gt; 1 &amp;&amp; i &lt; 100 -&gt; System.out.println("int is greater than 1 and less than 100");
default -&gt; System.out.println("int is greater or equal to 100");
case 1 -> System.out.println("int is 1");
case int i when i > 1 && i < 100 -> System.out.println("int is greater than 1 and less than 100");
default -> System.out.println("int is greater or equal to 100");
}
}
}