Java Lambda Variable Capture

A lambda expression can access final local variables or local-non-final-initialized-only-once variables.

Example

The following code shows that we can access and use the final local variables.

import java.util.function.Function;
// w w  w .j  a  va2 s  . c o m
public class Main {
  public static void main(String[] argv) {
    final String x = "Hello"; 
    Function<String,String> func1 = y -> {return y + " "+ x ;};
    System.out.println(func1.apply("java2s.com"));

  }
}

The code above generates the following result.

Example 2

The following code has a variable x which is not final but only initialized once. We can still use it in the lambda expression.

import java.util.function.Function;
/* w  ww.  j  a  va  2  s  .c  o m*/
public class Main {
  public static void main(String[] argv) {
    String x = "Hello"; 
    
    Function<String,String> func1 = y -> {return y + " "+ x ;};
    System.out.println(func1.apply("java2s.com"));
    
  }
}

The code above generates the following result.

Example 3

The following code shows that we cannot change the value defined outside lambda expression.

import java.util.function.Function;
//from  ww  w .ja  v a2 s  . c om
public class Main {
  public static void main(String[] argv) {
    String x = "Hello"; 
    
    Function<String,String> func1 = y -> {/*x="a";*/ return y + " "+ x ;};
    System.out.println(func1.apply("java2s.com"));
    
  }
}

The code above generates the following result.

Example 4

We can change the non-local variable in lambda expression.

import java.util.function.Function;
/*  ww w  .  java 2 s  .  c  o  m*/
public class Main {
  static String x = "Hello"; 
  public static void main(String[] argv) {

    
    Function<String,String> func1 = y -> {x="a"; return y + " "+ x ;};
    System.out.println(func1.apply("java2s.com"));
    
  }
}

The code above generates the following result.