How to pass a Java 8 lambda with a single parameter

user_39371 0
Viewed 17431

I want to simply pass a lambda (chunk of code) and execute it when I need to. How do I implement the method executeLambda(...) in the code below (as well what is the method signature):

public static void main(String[] args)
{
    String value = "Hello World";
    executeLambda(value -> print(value));
}

public static void print(String value)
{
    System.out.println(value);
}

public static void executeLambda(lambda)
{
    someCode();
    lamda.executeLambdaCode();
    someMoreCode();
}
java-8 lambda java
4 Answers

Your lambda takes one parameter, but you only pass the lambda to executeLambda, not the value. If you want the lambda to capture the local variable, don't write it taking a parameter, but if you do really want it to take one parameter, you would write it like this:

import java.util.function.Consumer;

public static void main(String[] args) {
    String message = "Hello World";
    executeLambda(message, value -> print(value));
}

public static void executeLambda(String value, Consumer<String> lambda) {
    lambda.accept(value);
}

If you want it to capture the value, then use Runnable, write the lambda as () -> print(value), and call it like runnable.run().

user_6360090 
public static void main(String[] args)
{
    String value = "Hello World";
    executeLambda(() -> print(value));
}

public static void print(String value)
{
    System.out.println(value);
}

public static void executeLambda(Runnable runnable)
{
    runnable.run();
}
user_16646240

By providing a reasonable parameter type. The method taking the lambda does not know about lambdas.

Instead you could pass a Callable object. And then your method has to invoke the call() method on that object! Alternatively, a Runnable or Consumer of String could be used (as a Callable is supposed to return a value - and the method you invoke is void).

user_15311240

Passing a byte[] and Runnable like:

public void doSmt(byte[] new_data, Runnable runnable) {
   for (byte datum : new_data) {
            LogI(String.valueOf(datum));
   }
   runnable.run();
}

Call:

byte[] new_data = new byte[10];    
doSmt(new_data, () -> {
     LogI("DA XONG");
});
user_111192810
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