CODEWITHSUNDEEP
javajava-stream
Jhutan Debnath
Jhutan Debnath

Reputation: 535

Using return statement inside java stream

Hi have two implementation some piece of code where I am modifying the strings using Java stream:

final List<String> strings = new ArrayList<>();
strings.add("abc");
strings.add("bca");
strings.add("xyz");

Method 1:
final List<String> modifiedStrings = strings.stream().map(a -> {
        String abc;
        abc = a.replace("a", "*");
        return abc;
    }).collect(Collectors.toList());

Method 2:
final List<String> modifiedStrings2 = strings.stream().map(a ->
        a.replace("a", "*")).collect(Collectors.toList());

I want to know if there is any performance difference between method one and method two.

Upvotes: 6

Views: 12777

Answers (2)

Thilo
Thilo

Reputation: 262724

No. This will compile to essentially the same bytecode. The second version is just a more concise way to write it.

Example code:

void foo(List<String> strings) {
  strings.stream()
      .map(
          a -> {
            String abc;
            abc = a.replace("a", "*");
            return abc;
          })
      .collect(Collectors.toList());
}

void bar(List<String> strings) {
  strings.stream().map(a -> a.replace("a", "*")).collect(Collectors.toList());
}

Corresponding lambda bytecode:

  private static java.lang.String lambda$bar$1(java.lang.String);
    descriptor: (Ljava/lang/String;)Ljava/lang/String;
    flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=3, locals=1, args_size=1
         0: aload_0
         1: ldc           #8                  // String a
         3: ldc           #9                  // String *
         5: invokevirtual #10                 // Method java/lang/String.replace:(Ljava/lang/CharSequence;Ljava/lang/CharSequence;)Ljava/lang/String;
         8: areturn
      LineNumberTable:
        line 18: 0

  private static java.lang.String lambda$foo$0(java.lang.String);
    descriptor: (Ljava/lang/String;)Ljava/lang/String;
    flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=3, locals=2, args_size=1
         0: aload_0
         1: ldc           #8                  // String a
         3: ldc           #9                  // String *
         5: invokevirtual #10                 // Method java/lang/String.replace:(Ljava/lang/CharSequence;Ljava/lang/CharSequence;)Ljava/lang/String;
         8: astore_1
         9: aload_1
        10: areturn
      LineNumberTable:
        line 11: 0
        line 12: 9

So, the bytecode is not quite the same - there is an extra astore_1 and aload_1 in the foo case; but this is likely irrelevant, as it can just be optimized away.

Upvotes: 17

thopaw
thopaw

Reputation: 4054

When the body of a lambda function is just one single expression the compiler determines the return type and value from this expression.

It is just syntactic sugar.

Upvotes: 1

Related Questions