java实现 流

1399852153 · 1399852153 · commit f5d493fca59d · 2019-03-07T20:29:17.000+08:00
diff --git a/src/main/java/second/stream/Process.java b/src/main/java/second/stream/Process.java
@@ -12,11 +12,6 @@ public class Process {
 
     EvalFunction evalFunction;
 
-    public Process(Process next, EvalFunction evalFunction) {
-        this.next = next;
-        this.evalFunction = evalFunction;
-    }
-
     public Process(EvalFunction evalFunction) {
         this.evalFunction = evalFunction;
     }
diff --git a/src/main/java/second/stream/Stream.java b/src/main/java/second/stream/Stream.java
@@ -89,7 +89,15 @@ public Stream<T> filter(Predicate<T> predicate) {
 
     @Override
     public Stream<T> limit(int n) {
-        return null;
+        Process lastProcess = this.process;
+        this.process = new Process(
+                ()-> {
+                    Stream stream = lastProcess.eval();
+                    return limit(n,stream);
+                }
+        );
+
+        return this;
     }
 
     @Override
@@ -146,6 +154,17 @@ private <R> R reduce(R initVal,Accumulate<R,T> accumulator,Stream<T> stream){
         return accumulator.apply(result,head);
     }
 
+    private Stream<T> limit(int num,Stream<T> stream){
+        if(num == 0){
+            return StreamInterface.makeEmptyStream();
+        }
+
+        return new Stream.Builder<T>()
+                .head(stream.head)
+                .process(new Process(()->limit(num-1,stream.eval())))
+                .build();
+    }
+
     private Stream<T> eval(){
         return this.process.eval();
     }
diff --git a/src/test/java/TestStream2.java b/src/test/java/TestStream2.java
@@ -11,9 +11,10 @@ public class TestStream2 {
     public static void main(String[] args){
         Stream<Integer> intStream = StreamGenerator.getIntegerStream(10);
 
-        intStream = intStream.filter(TestStream2::idOdd);
-        intStream = intStream.map(TestStream2::scaleTwo);
-        intStream = intStream.map(TestStream2::square);
+//        intStream = intStream.filter(TestStream2::idOdd);
+//        intStream = intStream.map(TestStream2::scaleTwo);
+//        intStream = intStream.map(TestStream2::square);
+//        intStream = intStream.limit(3);
 
         Integer sum = intStream.reduce(0,(v1,v2) -> v1 + v2);
 
