diff --git a/src/main/java/com/github/robtimus/tryparse/TryParse.java b/src/main/java/com/github/robtimus/tryparse/TryParse.java
index d817a40..a7ad818 100644
--- a/src/main/java/com/github/robtimus/tryparse/TryParse.java
+++ b/src/main/java/com/github/robtimus/tryparse/TryParse.java
@@ -46,7 +46,7 @@ public final class TryParse {
     private static final int DEFAULT_RADIX = 10;
 
     private TryParse() {
-        throw new Error("cannot create instances of " + getClass().getName()); //$NON-NLS-1$
+        throw new IllegalStateException("cannot create instances of " + getClass().getName()); //$NON-NLS-1$
     }
 
     // int
diff --git a/src/main/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBounds.java b/src/main/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBounds.java
index 03e79f6..cc03645 100644
--- a/src/main/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBounds.java
+++ b/src/main/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBounds.java
@@ -61,7 +61,7 @@ final class UnsignedMultiplyLongBounds {
     }
 
     private UnsignedMultiplyLongBounds() {
-        throw new Error("cannot create instances of " + getClass().getName()); //$NON-NLS-1$
+        throw new IllegalStateException("cannot create instances of " + getClass().getName()); //$NON-NLS-1$
     }
 
     static long get(int radix) {
diff --git a/src/test/java/com/github/robtimus/tryparse/TryParseBooleanTest.java b/src/test/java/com/github/robtimus/tryparse/TryParseBooleanTest.java
index 08bb6b6..1abe4e1 100644
--- a/src/test/java/com/github/robtimus/tryparse/TryParseBooleanTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/TryParseBooleanTest.java
@@ -23,11 +23,11 @@
 import java.util.Optional;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings({ "javadoc", "nls" })
-public class TryParseBooleanTest {
+@SuppressWarnings("nls")
+class TryParseBooleanTest {
 
     @Test
-    public void testTryParseBoolean() {
+    void testTryParseBoolean() {
         checkWithAndWithoutSubsequences(true, "true");
         checkWithAndWithoutSubsequences(true, "TRUE");
         checkWithAndWithoutSubsequences(false, "false");
diff --git a/src/test/java/com/github/robtimus/tryparse/TryParseCatchingTest.java b/src/test/java/com/github/robtimus/tryparse/TryParseCatchingTest.java
index ee3dac0..993de80 100644
--- a/src/test/java/com/github/robtimus/tryparse/TryParseCatchingTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/TryParseCatchingTest.java
@@ -49,11 +49,11 @@
 import java.util.OptionalDouble;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings({ "javadoc", "nls" })
-public class TryParseCatchingTest {
+@SuppressWarnings("nls")
+class TryParseCatchingTest {
 
     @Test
-    public void testParseDouble() {
+    void testParseDouble() {
         assertEquals(OptionalDouble.empty(), tryParseDouble(null));
         assertEquals(OptionalDouble.empty(), tryParseDouble(""));
         assertEquals(123.456, tryParseDouble("123.456").getAsDouble(), 0.00001);
@@ -61,7 +61,7 @@ public void testParseDouble() {
     }
 
     @Test
-    public void testParseURI() {
+    void testParseURI() {
         assertEquals(Optional.empty(), tryParseURI(null));
         // an empty URI is valid
         assertEquals(Optional.of(URI.create("http://example.org")), tryParseURI("http://example.org"));
@@ -69,7 +69,7 @@ public void testParseURI() {
     }
 
     @Test
-    public void testParseURL() throws MalformedURLException {
+    void testParseURL() throws MalformedURLException {
         assertEquals(Optional.empty(), tryParseURL(null));
         assertEquals(Optional.empty(), tryParseURL(""));
         assertEquals(Optional.of(new URL("http://example.org")), tryParseURL("http://example.org"));
@@ -77,7 +77,7 @@ public void testParseURL() throws MalformedURLException {
     }
 
     @Test
-    public void testParseInstant() {
+    void testParseInstant() {
         assertEquals(Optional.empty(), tryParseInstant(null));
         assertEquals(Optional.empty(), tryParseInstant(""));
         assertEquals(Optional.of(Instant.parse("2007-12-03T10:15:30.00Z")), tryParseInstant("2007-12-03T10:15:30.00Z"));
@@ -85,7 +85,7 @@ public void testParseInstant() {
     }
 
     @Test
-    public void testParseLocalDate() {
+    void testParseLocalDate() {
         assertEquals(Optional.empty(), tryParseLocalDate(null));
         assertEquals(Optional.empty(), tryParseLocalDate(""));
         assertEquals(Optional.of(LocalDate.of(2007, 12, 3)), tryParseLocalDate("2007-12-03"));
@@ -99,7 +99,7 @@ public void testParseLocalDate() {
     }
 
     @Test
-    public void testParseLocalDateTime() {
+    void testParseLocalDateTime() {
         assertEquals(Optional.empty(), tryParseLocalDateTime(null));
         assertEquals(Optional.empty(), tryParseLocalDateTime(""));
         assertEquals(Optional.of(LocalDateTime.of(2007, 12, 3, 10, 15, 30)), tryParseLocalDateTime("2007-12-03T10:15:30"));
@@ -113,7 +113,7 @@ public void testParseLocalDateTime() {
     }
 
     @Test
-    public void testParseLocalTime() {
+    void testParseLocalTime() {
         assertEquals(Optional.empty(), tryParseLocalTime(null));
         assertEquals(Optional.empty(), tryParseLocalTime(""));
         assertEquals(Optional.of(LocalTime.of(10, 15, 30)), tryParseLocalTime("10:15:30"));
@@ -127,7 +127,7 @@ public void testParseLocalTime() {
     }
 
     @Test
-    public void testParseOffsetDateTime() {
+    void testParseOffsetDateTime() {
         assertEquals(Optional.empty(), tryParseOffsetDateTime(null));
         assertEquals(Optional.empty(), tryParseOffsetDateTime(""));
         assertEquals(Optional.of(OffsetDateTime.of(2007, 12, 3, 10, 15, 30, 0, ZoneOffset.ofHours(1))),
@@ -143,7 +143,7 @@ public void testParseOffsetDateTime() {
     }
 
     @Test
-    public void testParseOffsetTime() {
+    void testParseOffsetTime() {
         assertEquals(Optional.empty(), tryParseOffsetTime(null));
         assertEquals(Optional.empty(), tryParseOffsetTime(""));
         assertEquals(Optional.of(OffsetTime.of(10, 15, 30, 0, ZoneOffset.ofHours(1))), tryParseOffsetTime("10:15:30+01:00"));
@@ -157,7 +157,7 @@ public void testParseOffsetTime() {
     }
 
     @Test
-    public void testParseZonedDateTime() {
+    void testParseZonedDateTime() {
         assertEquals(Optional.empty(), tryParseZonedDateTime(null));
         assertEquals(Optional.empty(), tryParseZonedDateTime(""));
         assertEquals(Optional.of(ZonedDateTime.of(2007, 12, 3, 10, 15, 30, 0, ZoneId.of("Europe/Paris"))),
@@ -173,7 +173,7 @@ public void testParseZonedDateTime() {
     }
 
     @Test
-    public void testParseTemporal() {
+    void testParseTemporal() {
         DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy");
         assertEquals(Optional.empty(), tryParseTemporal(null, formatter, LocalDate::from));
         assertEquals(Optional.empty(), tryParseTemporal("", formatter, LocalDate::from));
@@ -182,7 +182,7 @@ public void testParseTemporal() {
     }
 
     @Test
-    public void testParse() {
+    void testParse() {
         assertEquals(Optional.empty(), tryParse(null, o -> o));
         assertEquals(Optional.of(""), tryParse("", o -> o));
         assertEquals(Optional.of("foo"), tryParse("foo", o -> o));
diff --git a/src/test/java/com/github/robtimus/tryparse/TryParseIntTest.java b/src/test/java/com/github/robtimus/tryparse/TryParseIntTest.java
index 1beded8..ab7aa73 100644
--- a/src/test/java/com/github/robtimus/tryparse/TryParseIntTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/TryParseIntTest.java
@@ -23,11 +23,11 @@
 import java.util.OptionalInt;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings({ "javadoc", "nls" })
-public class TryParseIntTest {
+@SuppressWarnings("nls")
+class TryParseIntTest {
 
     @Test
-    public void testTryParseInt() {
+    void testTryParseInt() {
         checkNegativeNumber(-128);
         for (int i = -32; i < 0; i++) {
             checkNegativeNumber(i);
diff --git a/src/test/java/com/github/robtimus/tryparse/TryParseLongTest.java b/src/test/java/com/github/robtimus/tryparse/TryParseLongTest.java
index 76ac90b..798f43c 100644
--- a/src/test/java/com/github/robtimus/tryparse/TryParseLongTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/TryParseLongTest.java
@@ -24,11 +24,11 @@
 import java.util.OptionalLong;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings({ "javadoc", "nls" })
-public class TryParseLongTest {
+@SuppressWarnings("nls")
+class TryParseLongTest {
 
     @Test
-    public void testTryParseLong() {
+    void testTryParseLong() {
         checkNegativeNumber(-128);
         for (long i = -32; i < 0; i++) {
             checkNegativeNumber(i);
diff --git a/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedIntTest.java b/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedIntTest.java
index cbd214f..5bd37e6 100644
--- a/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedIntTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedIntTest.java
@@ -23,13 +23,13 @@
 import java.util.OptionalInt;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings({ "javadoc", "nls" })
-public class TryParseUnsignedIntTest {
+@SuppressWarnings("nls")
+class TryParseUnsignedIntTest {
 
     private static final long MAX_UNSIGNED_INT_VALUE = 0xFFFF_FFFFL;
 
     @Test
-    public void testTryParseUnsignedInt() {
+    void testTryParseUnsignedInt() {
         checkNegativeNumber(-128);
         for (int i = -32; i < 0; i++) {
             checkNegativeNumber(i);
diff --git a/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedLongTest.java b/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedLongTest.java
index 1d71be4..95ff388 100644
--- a/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedLongTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/TryParseUnsignedLongTest.java
@@ -25,13 +25,13 @@
 import java.util.OptionalLong;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings({ "javadoc", "nls" })
-public class TryParseUnsignedLongTest {
+@SuppressWarnings("nls")
+class TryParseUnsignedLongTest {
 
     private static final BigInteger MAX_UNSIGNED_LONG_VALUE = BigInteger.valueOf(2).pow(64).subtract(BigInteger.ONE);
 
     @Test
-    public void testTryParseUnsignedLong() {
+    void testTryParseUnsignedLong() {
         checkNegativeNumber(-128);
         for (long i = -32; i < 0; i++) {
             checkNegativeNumber(i);
diff --git a/src/test/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBoundsTest.java b/src/test/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBoundsTest.java
index 0fd0d22..4259fb7 100644
--- a/src/test/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBoundsTest.java
+++ b/src/test/java/com/github/robtimus/tryparse/UnsignedMultiplyLongBoundsTest.java
@@ -22,13 +22,12 @@
 import java.math.BigInteger;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings("javadoc")
-public class UnsignedMultiplyLongBoundsTest {
+class UnsignedMultiplyLongBoundsTest {
 
     private static final BigInteger MAX_UNSIGNED_LONG_VALUE = BigInteger.valueOf(2).pow(64).subtract(BigInteger.ONE);
 
     @Test
-    public void testGet() {
+    void testGet() {
         for (int radix = Character.MIN_RADIX; radix <= Character.MAX_RADIX; radix++) {
             long expected = MAX_UNSIGNED_LONG_VALUE.divide(BigInteger.valueOf(radix)).longValueExact();
             assertEquals(expected, UnsignedMultiplyLongBounds.get(radix));
@@ -36,7 +35,7 @@ public void testGet() {
     }
 
     @Test
-    public void testGetRadixToHigh() {
+    void testGetRadixToHigh() {
         assertThrows(IndexOutOfBoundsException.class, () -> UnsignedMultiplyLongBounds.get(Character.MAX_RADIX + 1));
     }
 }