String concat 성능 비교(StringBuilder를 쓰자)

[boojongmin]

소스

import org.springframework.util.StopWatch;

import java.util.Arrays;
import java.util.function.BooleanSupplier;

public class LambdaMain {
    public static void main(String[] args) {

        var arr = new String[100_000];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = "" + Math.random();
        }

        var sw = new StopWatch();

        sw.start();
        var result = "";
        for (int i = 0; i < arr.length; i++) {
            result += arr[i];
        }
        sw.stop();
        System.out.println(">>> String +: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        var buffer = new StringBuffer();
        for (int i = 0; i < arr.length; i++) {
            buffer.append(arr[i]);
        }
        result = buffer.toString();
        sw.stop();
        System.out.println(">>> StringBuffer without capacity: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        result = String.join("", arr);
        sw.stop();
        System.out.println(">>> String.join: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        var builder = new StringBuilder();
        for (int i = 0; i < arr.length; i++) {
            builder.append(arr[i]);
        }
        result = builder.toString();
        sw.stop();
        System.out.println(">>> StringBuilder without capacity: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        builder = new StringBuilder(1_000_000);
        for (int i = 0; i < arr.length; i++) {
            builder.append(arr[i]);
        }
        result = builder.toString();
        sw.stop();
        System.out.println(">>> StringBuilder with capacity: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        buffer = new StringBuffer(1_000_000);
        for (int i = 0; i < arr.length; i++) {
            buffer.append(arr[i]);
        }
        result = buffer.toString();
        sw.stop();
        System.out.println(">>> StringBuffer with capacity: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        result = String.join("", arr);
        sw.stop();
        System.out.println(">>> String.join: " + sw.getLastTaskTimeMillis() + "ms");

        sw.start();
        result = "";
        for (int i = 0; i < arr.length; i++) {
            result += arr[i];
        }
        sw.stop();
        System.out.println(">>> String +: " + sw.getLastTaskTimeMillis() + "ms");


    }
}

결과

(핫스팟 영향이 있음)

String +: 10173ms
StringBuffer without capacity: 9ms
String.join: 13ms
StringBuilder without capacity: 2ms
StringBuilder with capacity: 2ms
StringBuffer with capacity: 3ms
String.join: 4ms