collections

whatsmars-common/src/test/java/org/hongxi/java/util/collections/ArrListTest.java

+package org.hongxi.java.util.collections;
+
+/**
+ * @author shenhongxi 2019/8/12
+ */
+public class ArrListTest {
+
+    public static void main(String[] args) {
+        SimpleArrList arrList = new SimpleArrList();
+        arrList.add(1);
+        arrList.add(2);
+        arrList.add(3);
+        arrList.add(null);
+        System.out.println(arrList);
+    }
+}

whatsmars-common/src/test/java/org/hongxi/java/util/collections/SimpleArrList.java

+package org.hongxi.java.util.collections;
+
+import java.util.Arrays;
+
+/**
+ * @author shenhongxi 2019/8/12
+ */
+public class SimpleArrList<E> {
+
+    private static final int DEFAULT_CAPACITY = 10;
+
+    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
+
+    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
+
+    Object[] elements;
+    int size;
+
+    SimpleArrList() {
+        elements = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
+    }
+
+    void add(E e) {
+        ensureCapacityInternal(size + 1);
+        elements[size++] = e;
+    }
+
+    private void ensureCapacityInternal(int minCapacity) {
+        if (elements == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
+            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
+        }
+
+        ensureExplicitCapacity(minCapacity);
+    }
+
+    private void ensureExplicitCapacity(int minCapacity) {
+        if (minCapacity - elements.length > 0)
+            grow(minCapacity);
+    }
+
+    private void grow(int minCapacity) {
+        int oldCapacity = elements.length;
+        int newCapacity = oldCapacity + (oldCapacity >> 1);
+        if (newCapacity - minCapacity < 0)
+            newCapacity = minCapacity;
+        if (newCapacity - MAX_ARRAY_SIZE > 0)
+            newCapacity = hugeCapacity(minCapacity);
+        elements = Arrays.copyOf(elements, newCapacity);
+    }
+
+    private static int hugeCapacity(int minCapacity) {
+        if (minCapacity < 0) // overflow
+            throw new OutOfMemoryError();
+        return (minCapacity > MAX_ARRAY_SIZE) ?
+                Integer.MAX_VALUE :
+                MAX_ARRAY_SIZE;
+    }
+
+    @Override
+    public String toString() {
+        if (size > 0) {
+            StringBuilder s = new StringBuilder();
+            for (int i = 0; i < size; i++) {
+                s.append(elements[i]);
+                if (i < size - 1) {
+                    s.append(", ");
+                }
+            }
+            return "[" + s + "]";
+        }
+        return "[]";
+    }
+}