custom stream draft implementation

anton-liauchuk · anton-liauchuk · commit a2dc890869c6 · 2019-09-22T15:38:08.000+03:00
diff --git a/custom-stream/build.gradle b/custom-stream/build.gradle
@@ -0,0 +1,16 @@
+plugins {
+    id 'java'
+}
+
+group 'custom-stream'
+version '1.0-SNAPSHOT'
+
+sourceCompatibility = 1.8
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testCompile group: 'junit', name: 'junit', version: '4.12'
+}
diff --git a/custom-stream/src/main/java/ReferencePipeline.java b/custom-stream/src/main/java/ReferencePipeline.java
@@ -0,0 +1,94 @@
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+public class ReferencePipeline implements Stream {
+
+    protected ReferencePipeline previousStage;
+
+    private List<StreamObject> objects;
+
+    private ReferencePipeline(List<StreamObject> objects) {
+        this.objects = objects;
+    }
+
+    public ReferencePipeline() {
+    }
+
+    public Sink opWrapSink(Sink sink) {
+        throw new UnsupportedOperationException();
+    }
+
+    public static ReferencePipeline of(List<StreamObject> objects) {
+        return new ReferencePipeline(objects);
+    }
+
+    public Stream filter(Predicate<StreamObject> predicate) {
+        return new Operation(this) {
+            @Override
+            public Sink opWrapSink(Sink sink) {
+                return new ChainedReference(sink) {
+
+                    @Override
+                    public void accept(Object o) {
+                        if (predicate.test((StreamObject) o))
+                            downstream.accept(o);
+                    }
+                };
+            }
+        };
+    }
+
+    public Stream map(Function function) {
+        return new Operation(this) {
+            @Override
+            public Sink opWrapSink(Sink sink) {
+                return new ChainedReference(sink) {
+
+                    @Override
+                    public void accept(Object o) {
+                        downstream.accept(function.apply(o));
+                    }
+                };
+            }
+        };
+    }
+
+    public List<Object> toList() {
+        final List<Object> result = new ArrayList<>();
+
+        Sink finalSink = o -> result.add(o);
+
+        ReferencePipeline previousStage = this;
+        Sink sink = finalSink;
+
+        while (previousStage.previousStage != null) {
+            sink = previousStage.opWrapSink(sink);
+            previousStage = previousStage.previousStage;
+        }
+
+        for (StreamObject object : previousStage.objects) {
+            sink.accept(object);
+        }
+
+        return result;
+    }
+
+    abstract class Operation extends ReferencePipeline {
+
+        public Operation(ReferencePipeline previousStage) {
+            this.previousStage = previousStage;
+        }
+    }
+
+    abstract class ChainedReference implements Sink {
+        protected final Sink downstream;
+
+        public ChainedReference(Sink downstream) {
+            this.downstream = Objects.requireNonNull(downstream);
+        }
+    }
+
+}
diff --git a/custom-stream/src/main/java/Sink.java b/custom-stream/src/main/java/Sink.java
@@ -0,0 +1,5 @@
+import java.util.function.Consumer;
+
+interface Sink extends Consumer {
+
+}
diff --git a/custom-stream/src/main/java/Stream.java b/custom-stream/src/main/java/Stream.java
@@ -0,0 +1,9 @@
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+interface Stream {
+    Stream filter(Predicate<StreamObject> predicate);
+    Stream map(Function<StreamObject, Integer> function);
+    List<Object> toList();
+}
diff --git a/custom-stream/src/main/java/StreamObject.java b/custom-stream/src/main/java/StreamObject.java
@@ -0,0 +1,21 @@
+public class StreamObject {
+
+    private int id;
+    private String name;
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}
diff --git a/custom-stream/src/test/java/StreamTest.java b/custom-stream/src/test/java/StreamTest.java
@@ -0,0 +1,31 @@
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class StreamTest {
+
+    @Test
+    public void debugStream() {
+        StreamObject object0 = new StreamObject();
+        object0.setId(0);
+        object0.setName("0");
+
+        StreamObject object1 = new StreamObject();
+        object1.setId(1);
+        object1.setName("1");
+
+        List<StreamObject> collection = Arrays.asList(object0, object1);
+//        final List<Integer> collect = collection.stream()
+//                .filter(streamObject -> streamObject.getId() == 0)
+//                .map(StreamObject::getId)
+//                .collect(Collectors.toList());
+
+        ReferencePipeline.of(collection)
+                .filter(streamObject -> streamObject.getId() == 0)
+                .map(StreamObject::getId)
+                .toList();
+    }
+
+}

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +import java.util.function.Consumer;
++
 +interface Sink extends Consumer {
++
 +}