下面2 段代码性能上哪个更优？

Dear 丶 2024-02-23 07:49 14阅读 0赞

##### 1.问题 #####

今天在知乎看到一个很有意思的问题，记录下

private String testStr = "This is a test string";
        	private char[] testChar = {
         'a', 'b', 'c', 'd' };
        
        	// 代码块1
            for (int i = 0; i < testStr.length(); i++) {
        
                for (int j = 0; j < testChar.length; j++) {
        
                    if (testStr.charAt(i) == testChar[j]) {
        
                        return true;
                    }
                }
            }
            // 代码块2
            for (int i = 0; i < testStr.length(); i++) {
        
                for (int j = 0; j < testChar.length; j++) {
        
                    if (testStr.charAt(i) == testChar[j]) {
        
                        return true;
                    }
                }
            }

##### 2.性能测试 #####

import org.openjdk.jmh.annotations.*;
    import java.util.concurrent.TimeUnit;
    
    @State(Scope.Benchmark)
    @BenchmarkMode(Mode.AverageTime)
    @OutputTimeUnit(TimeUnit.NANOSECONDS)
    public class CharComparisonBenchmark {
        
    
        public static void main(String[] args) throws RunnerException {
        
            Options opt = new OptionsBuilder().include(For2Test.class.getSimpleName()).warmupIterations(1).measurementIterations(1).forks(1).build();
            new Runner(opt).run();
        }
    
        private static final String testStr = "This is a test string";
        private static final char[] testChar = {
         'a', 'b', 'c', 'd' };
    
        @Benchmark
        public boolean testCharComparison1() {
        
            for (int i = 0; i < testStr.length(); i++) {
        
                for (int j = 0; j < testChar.length; j++) {
        
                    if (testStr.charAt(i) == testChar[j]) {
        
                        return true;
                    }
                }
            }
            return false;
        }
    
        @Benchmark
        public boolean testCharComparison2() {
        
            for (int i = 0; i < testStr.length(); i++) {
        
                for (int j = 0; j < testChar.length; j++) {
        
                    if (testStr.charAt(i) == testChar[j]) {
        
                        return true;
                    }
                }
            }
            return false;
        }
    }

测试结果基本符合预期，当时完备的测试数据量应该是随机的，且字符数较多，有兴趣的同学可以继续研究下  
![在这里插入图片描述][8f0000b841cc465d9a7254fc50cbd200.png]

[8f0000b841cc465d9a7254fc50cbd200.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/23/971689af86514f0a82615cecbdd89418.png