classlib: implement String.chars() (#872)

classlib/src/main/java/org/teavm/classlib/java/lang/TString.java

@@ -31,6 +31,8 @@ import org.teavm.classlib.java.util.TComparator;
 import org.teavm.classlib.java.util.TFormatter;
 import org.teavm.classlib.java.util.TLocale;
 import org.teavm.classlib.java.util.regex.TPattern;
+import org.teavm.classlib.java.util.stream.TIntStream;
+import org.teavm.classlib.java.util.stream.intimpl.TStringCharsStream;
 import org.teavm.dependency.PluggableDependency;
 import org.teavm.interop.NoSideEffects;
 
@@ -587,6 +589,10 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return array;
     }
 
+    public TIntStream chars() {
+        return new TStringCharsStream(this);
+    }
+
     public static String valueOf(Object obj) {
         return obj != null ? obj.toString() : "null";
     }

classlib/src/main/java/org/teavm/classlib/java/util/stream/intimpl/TStringCharsStream.java

@@ -0,0 +1,49 @@
+/*
+ *  Copyright 2023 JFronny.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.classlib.java.util.stream.intimpl;
+
+import java.util.Objects;
+import java.util.function.IntPredicate;
+import org.teavm.classlib.java.lang.TString;
+
+public class TStringCharsStream extends TSimpleIntStreamImpl {
+    private final TString string;
+    private int index;
+
+    public TStringCharsStream(TString string) {
+        this.string = Objects.requireNonNull(string);
+    }
+
+    @Override
+    public boolean next(IntPredicate consumer) {
+        while (index < string.length()) {
+            if (!consumer.test(string.charAt(index++))) {
+                break;
+            }
+        }
+        return index < string.length();
+    }
+
+    @Override
+    protected int estimateSize() {
+        return string.length();
+    }
+
+    @Override
+    public long count() {
+        return string.length();
+    }
+}

tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java

@@ -372,4 +372,10 @@ public class StringTest {
         assertFalse(new String(new char[] { ' ', 'x', ' ' }).isBlank());
         assertFalse(new String(new char[] { 'a', ' ' }).isBlank());
     }
+
+    @Test
+    public void testChars() {
+        assertEquals(0, "".chars().toArray().length);
+        assertArrayEquals(new int[] {'A', 'B', 'C', '1', '2', '3'}, "ABC123".chars().toArray());
+    }
 }