字节码测试

对比过程

编写的源程序如下，分别使用了匿名类调用、lambda、函数引用，对象内部的函数引用四种方式进行测试。

package com.test.function.call;
public class Test {
    public String name(String param) {
        return String.format("this::name(%s)", param);
    }
    public void call(){
        print(this::name);
    }
    @FunctionalInterface
    public interface Func<T, R> {
        R apply(T t);
    }
    public static void print(Func<String, String> func) {
        func.apply("2");
    }
    public static void main(String[] args) {
        Test test = new Test();
        System.out.println();
        print(new Func<String, String>() {
            @Override
            public String apply(String s) {
                return test.name(s);
            }
        });
        System.out.println();
        print((s) -> test.name(s));
        System.out.println();
        print(test::name);
        System.out.println();
        test.call();
        System.out.println();
    }
}

先将程序编译为class文件，然后使用javap -v Test.class，查看详细字节码信息

 0: new           #9                  // class com/test/function/call/Test
 3: dup
 4: invokespecial #10                 // Method "<init>":()V
 7: astore_1
 8: getstatic     #11                 // Field java/lang/System.out:Ljava/io/PrintStream;
11: invokevirtual #12                 // Method java/io/PrintStream.println:()V
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
14: new           #13                 // class com/test/function/call/Test$1
17: dup
18: aload_1
19: invokespecial #14                 // Method com/test/function/call/Test$1."<init>":(Lcom/test/function/call/Test;)V
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
22: invokestatic  #6                  // Method print:(Lcom/test/function/call/Test$Func;)V
25: getstatic     #11                 // Field java/lang/System.out:Ljava/io/PrintStream;
28: invokevirtual #12                 // Method java/io/PrintStream.println:()V
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
31: aload_1
32: invokedynamic #15,  0             // InvokeDynamic #1:apply:(Lcom/test/function/call/Test;)Lcom/test/function/call/Test$Func;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
37: invokestatic  #6                  // Method print:(Lcom/test/function/call/Test$Func;)V
40: getstatic     #11                 // Field java/lang/System.out:Ljava/io/PrintStream;
43: invokevirtual #12                 // Method java/io/PrintStream.println:()V
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
46: aload_1
47: dup
48: invokestatic  #16                 // Method java/util/Objects.requireNonNull:(Ljava/lang/Object;)Ljava/lang/Object;
51: pop
52: invokedynamic #5,  0              // InvokeDynamic #0:apply:(Lcom/test/function/call/Test;)Lcom/test/function/call/Test$Func;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
57: invokestatic  #6                  // Method print:(Lcom/test/function/call/Test$Func;)V
60: getstatic     #11                 // Field java/lang/System.out:Ljava/io/PrintStream;
63: invokevirtual #12                 // Method java/io/PrintStream.println:()V
66: aload_1
67: invokevirtual #17                 // Method call:()V
70: getstatic     #11                 // Field java/lang/System.out:Ljava/io/PrintStream;
73: invokevirtual #12                 // Method java/io/PrintStream.println:()V
76: return

method的字节码

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
0: aload_0
1: invokedynamic #5,  0              // InvokeDynamic #0:apply:(Lcom/test/function/call/Test;)Lcom/test/function/call/Test$Func;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6: invokestatic  #6                  // Method print:(Lcom/test/function/call/Test$Func;)V
9: return

可以统计到以下结果：

• 匿名类的方式使用了4个字节码，且使用了new指令
• lambda的方式使用两个字节码
• 函数引用的方式使用5个字节码
• 对象内的函数引用方式使用两个字节码

  结论

  除了匿名类的方式外，另外三种方式都非常高效。特殊情况是：在对象外使用时，尽量考虑lambda的方式，性能略高于函数引用。

  Benchmark测试

  对比过程

  编写的源程序如下，借助了Jmh工具，分别使用了匿名类调用、lambda、函数引用，对象内部的函数引用四种方式进行测试。 ``` import org.openjdk.jmh.annotations.*; import org.openjdk.jmh.runner.Runner; import org.openjdk.jmh.runner.RunnerException; import org.openjdk.jmh.runner.options.Options; import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime) @OutputTimeUnit(TimeUnit.NANOSECONDS) @State(Scope.Thread) public class JmhTest { private Test test;

public String name(String param) {
    return String.format("this::name(%s)", param);
}
public void call() {
    print(this::name);
}
@FunctionalInterface
public interface Func<T, R> {
    R apply(T t);
}
public static void print(Func<String, String> func) {
    func.apply("2");
}
@Setup(Level.Trial)
public void init() {
    test = new Test();
}
@Benchmark
public void printNewFunc() {
    print(new Func<String, String>() {
        @Override
        public String apply(String s) {
            return name(s);
        }
    });
}
@Benchmark
public void printLambda() {
    print((s) -> name(s));
}
@Benchmark
public void printFunctionInterface1() {
    print(test::name);
}
@Benchmark
public void printFunctionInterface2() {
    print(this::name);
}
public static void test() throws RunnerException {
    Options options = new OptionsBuilder().include(JmhTest.class.getName() + ".*")
            .warmupIterations(5).measurementIterations(5).forks(1).build();
    new Runner(options).run();
}
public static void main(String[] args) throws RunnerException {
    test();
}

}

``` 在Idea中Run运行，结果如下：

结论

匿名类由于存在new指令，所以执行时间高于其他方式，而另外三种性能差别不大，但是lambda略优于另外两种。