# Use Functional Interfaces
# Properties
| Property | Value |
|---|---|
| Rule ID | FunctionalInterface |
| First seen in jSparrow version | 1.0.0 |
| Minimum Java version | 8 |
| Remediation cost | 5 min |
| Links |
# Description
Converts anonymous inner classes to equivalent lambda expressions.
# Benefits
Increases the performance, because lesser objects need to be created. Improves readability because a lot of boilerplate code will be removed.
# Code Changes
# Remove anonymous instantiation of functional interface
Pre
Runnable runnable = new Runnable() {
@Override
public void run() {
System.out.println("xx");
}
};
Post
Runnable runnable = () -> {
System.out.println("xx");
};
# Rename variables if they are present in the scope outside of the inner class
Pre
int a = 5;
AFunctionalInterface foo = new AFunctionalInterface() {
@Override
public void method(int a) {
int b = a;
}
};
Post
int a = 5;
AFunctionalInterface foo = (int a1) -> {
int b = a1;
};
# Bytecode JDK 1.8
Pre
public Runnable runableWithAnonymousClass() {
Runnable r = new Runnable() {
public void run() {
System.out.println("Anonymous class");
}
};
return r;
}
0 new #2 <at/splendit/AnonymousClassesToLambdaExpressions$1>
3 dup
4 aload_0
5 invokespecial #3 <at/splendit/AnonymousClassesToLambdaExpressions$1.<init>>
8 astore_1
9 aload_1
10 areturn
Post
public Runnable runableWithLambda() {
Runnable r = () -> {
System.out.println("Lambda");
};
return r;
}
0 invokedynamic #4 <run, BootstrapMethods #0>
5 astore_1
6 aload_1
7 areturn
0 getstatic #5 <java/lang/System.out>
3 ldc #6 <Lambda>
5 invokevirtual #7 <java/io/PrintStream.println>
8 return
# Limitations
Variables that are used inside the anonymous class must be effectively final.
Automatic Application of This Rule
The automatic application of this rule is supported in the following jSparrow version:
# Tags
1
You & jSparrow
