Array or List in Java. Which is faster?

Question

I have to keep thousands of strings in memory to be accessed serially in Java. Should I store them in an array or should I use some kind of List ?

Since arrays keep

Answer 1

None of the answers had information that I was interested in - repetitive scan of the same array many many times. Had to create a JMH test for this.

Results (Java 1.8.0_66 x32, iterating plain array is at least 5 times quicker than ArrayList):

Benchmark                    Mode  Cnt   Score   Error  Units
MyBenchmark.testArrayForGet  avgt   10   8.121 ? 0.233  ms/op
MyBenchmark.testListForGet   avgt   10  37.416 ? 0.094  ms/op
MyBenchmark.testListForEach  avgt   10  75.674 ? 1.897  ms/op

Test

package my.jmh.test;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;

@State(Scope.Benchmark)
@Fork(1)
@Warmup(iterations = 5, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 10)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
public class MyBenchmark {

    public final static int ARR_SIZE = 100;
    public final static int ITER_COUNT = 100000;

    String arr[] = new String[ARR_SIZE];
    List list = new ArrayList<>(ARR_SIZE);

    public MyBenchmark() {
        for( int i = 0; i < ARR_SIZE; i++ ) {
            list.add(null);
        }
    }

    @Benchmark
    public void testListForEach() {
        int count = 0;
        for( int i = 0; i < ITER_COUNT; i++ ) {
            for( String str : list ) {
                if( str != null )
                    count++;
            }
        }
        if( count > 0 )
            System.out.print(count);
    }

    @Benchmark
    public void testListForGet() {
        int count = 0;
        for( int i = 0; i < ITER_COUNT; i++ ) {
            for( int j = 0; j < ARR_SIZE; j++ ) {
                if( list.get(j) != null )
                    count++;
            }
        }
        if( count > 0 )
            System.out.print(count);
    }

    @Benchmark
    public void testArrayForGet() {
        int count = 0;
        for( int i = 0; i < ITER_COUNT; i++ ) {
            for( int j = 0; j < ARR_SIZE; j++ ) {
                if( arr[j] != null )
                    count++;
            }
        }
        if( count > 0 )
            System.out.print(count);
    }

}