jdk-24/test/jdk/java/lang/String/CompactString/MaxSizeUTF16String.java

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import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

import java.nio.charset.StandardCharsets;

/*
 * @test
 * @bug 8077559 8321180
 * @summary Tests Compact String for maximum size strings
 * @requires os.maxMemory >= 7g & vm.bits == 64
 * @run junit/othervm -XX:+CompactStrings -Xmx7g MaxSizeUTF16String
 * @run junit/othervm -XX:-CompactStrings -Xmx7g MaxSizeUTF16String
 */

public class MaxSizeUTF16String {

    private final static int MAX_UTF16_STRING_LENGTH = Integer.MAX_VALUE / 2;

    private final static String EXPECTED_OOME_MESSAGE = "UTF16 String size is";

    // Create a large UTF-8 byte array with a single non-latin1 character
    private static byte[] generateUTF8Data(int byteSize) {
        byte[] nonAscii = "\u0100".getBytes(StandardCharsets.UTF_8);
        byte[] arr = new byte[byteSize];
        System.arraycopy(nonAscii, 0, arr, 0, nonAscii.length); // non-latin1 at start
        return arr;
    }

    // Create a large char array with a single non-latin1 character
    private static char[] generateCharData(int size) {
        char[] nonAscii = "\u0100".toCharArray();
        char[] arr = new char[size];
        System.arraycopy(nonAscii, 0, arr, 0, nonAscii.length); // non-latin1 at start
        return arr;
    }

    @Test
    public void testMaxUTF8() {
        // Overly large UTF-8 data with 1 non-latin1 char
        final byte[] large_utf8_bytes = generateUTF8Data(MAX_UTF16_STRING_LENGTH + 1);
        int[] sizes = new int[] {
                MAX_UTF16_STRING_LENGTH + 1,
                MAX_UTF16_STRING_LENGTH,
                MAX_UTF16_STRING_LENGTH - 1};
        for (int size : sizes) {
            System.err.println("Checking max UTF16 string len: " + size);
            try {
                // Use only part of the UTF-8 byte array
                new String(large_utf8_bytes, 0, size, StandardCharsets.UTF_8);
                if (size >= MAX_UTF16_STRING_LENGTH) {
                    fail("Expected OutOfMemoryError with message prefix: " + EXPECTED_OOME_MESSAGE);
                }
            } catch (OutOfMemoryError ex) {
                if (!ex.getMessage().startsWith(EXPECTED_OOME_MESSAGE)) {
                    fail("Failed: Not the OutOfMemoryError expected", ex);
                }
            }
        }
    }

    @Test
    public void testMaxCharArray() {
        // Overly large UTF-8 data with 1 non-latin1 char
        final char[] large_char_array = generateCharData(MAX_UTF16_STRING_LENGTH + 1);
        int[] sizes = new int[]{
                MAX_UTF16_STRING_LENGTH + 1,
                MAX_UTF16_STRING_LENGTH,
                MAX_UTF16_STRING_LENGTH - 1};
        for (int size : sizes) {
            System.err.println("Checking max UTF16 string len: " + size);
            try {
                // Large char array with 1 non-latin1 char
                new String(large_char_array, 0, size);
                if (size >= MAX_UTF16_STRING_LENGTH) {
                    fail("Expected OutOfMemoryError with message prefix: " + EXPECTED_OOME_MESSAGE);
                }
            } catch (OutOfMemoryError ex) {
                if (!ex.getMessage().startsWith(EXPECTED_OOME_MESSAGE)) {
                    throw new RuntimeException("Wrong exception message: " + ex.getMessage(), ex);
                }
            }
        }
    }
}