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How to do efficient debugging in Java lambda expressions?

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Efficient debugging of Lambda expressions: IntelliJ IDEA Debugger: Set breakpoints on variable declarations or methods, inspect internal variables and state, and see the actual implementation class. Java 9 JVMTI: Connect to the runtime JVM to get identifiers, inspect bytecode, set breakpoints, and monitor variables and status during execution.

如何在Java lambda表达式中进行有效的调试?

How to effectively debug in Java Lambda expressions

Lambda expressions can greatly simplify Java code, but in Debugging aspects pose challenges. Here are tips for effectively debugging them:

Using the IntelliJ IDEA Debugger

IntelliJ IDEA provides excellent debugging capabilities for Lambda expressions. In IDEA:

  • A breakpoint is set on the variable or method declaration of a lambda expression.
  • Inspect the internal variables and status of a Lambda expression in the debugger.
  • View the actual implementation class of lambda expression.

Java Virtual Machine Tool Interface (JVMTI) for Java 9

Starting with Java 9, there is a new tool called JVMTI that allows Go deeper when debugging lambda expressions. Use JVMTI:

  • Connect to the runtime JVM and obtain the identifier of the lambda expression.
  • Inspect the bytecode of the lambda expression and set breakpoints.
  • Monitor variables and status during lambda expression execution.

Practical case

Consider the following lambda expression:

Map map = new HashMap<>();
map.computeIfAbsent("key", k -> 42);

Debugging example

In IntelliJ IDEA, set a breakpoint on map.computeIfAbsent. When the breakpoint is reached, the debugger displays the source code and actual implementation class of the lambda expression. You can check the value of k and monitor the execution of the lambda expression.

JVMTI Example

Using JVMTI, you can:

  1. Connect to the runtime JVM and obtain the identifier of a lambda expression.
  2. Find and load the bytecode of the lambda expression.
  3. Set a breakpoint and monitor variables and status during lambda expression execution.

Extra Tip

  • Use explicit type declarations to improve readability when debugging.
  • Broken complex lambda expressions into smaller parts.
  • Use logging or print statements to view the intermediate status of lambda expression execution.
  • Use bytecode decompilation tools to see the actual implementation of lambda expressions.

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