小傅哥，文章代码更新。晚上好!

面经手册 · 第7篇《ArrayList也这么多知识？一个指定位置插入就把谢飞机面晕了！》
XYZ52000 · Aug 28, 2020 · 287ab7d · 287ab7d
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diff --git a/.gitignore b/.gitignore
@@ -1,2 +1,4 @@
 /interview.iml
 /interview-04/interview-04.iml
+/interview-07/interview-07.iml
+/interview-05/interview-05.iml
diff --git a/README.md b/README.md
@@ -14,4 +14,5 @@
 4. [面经手册 · 第3篇《HashMap核心知识，扰动函数、负载因子、扩容链表拆分，深度学习》](https://bugstack.cn/interview/2020/08/07/%E9%9D%A2%E7%BB%8F%E6%89%8B%E5%86%8C-%E7%AC%AC3%E7%AF%87-HashMap%E6%A0%B8%E5%BF%83%E7%9F%A5%E8%AF%86-%E6%89%B0%E5%8A%A8%E5%87%BD%E6%95%B0-%E8%B4%9F%E8%BD%BD%E5%9B%A0%E5%AD%90-%E6%89%A9%E5%AE%B9%E9%93%BE%E8%A1%A8%E6%8B%86%E5%88%86-%E6%B7%B1%E5%BA%A6%E5%AD%A6%E4%B9%A0.html)
 5. [面经手册 · 第4篇《HashMap数据插入、查找、删除、遍历，源码分析》](https://bugstack.cn/interview/2020/08/13/%E9%9D%A2%E7%BB%8F%E6%89%8B%E5%86%8C-%E7%AC%AC4%E7%AF%87-HashMap%E6%95%B0%E6%8D%AE%E6%8F%92%E5%85%A5-%E6%9F%A5%E6%89%BE-%E5%88%A0%E9%99%A4-%E9%81%8D%E5%8E%86-%E6%BA%90%E7%A0%81%E5%88%86%E6%9E%90.html)
 6. [面经手册 · 第5篇《看图说话，讲解2-3平衡树「红黑树的前身」》](https://bugstack.cn/interview/2020/08/16/%E9%9D%A2%E7%BB%8F%E6%89%8B%E5%86%8C-%E7%AC%AC5%E7%AF%87-%E7%9C%8B%E5%9B%BE%E8%AF%B4%E8%AF%9D-%E8%AE%B2%E8%A7%A32-3%E5%B9%B3%E8%A1%A1%E6%A0%91-%E7%BA%A2%E9%BB%91%E6%A0%91%E7%9A%84%E5%89%8D%E8%BA%AB.html)
-7 [面经手册 · 第6篇《带着面试题学习红黑树操作原理，解析什么时候染色、怎么进行旋转、与2-3树有什么关联》](https://bugstack.cn/interview/2020/08/20/%E9%9D%A2%E7%BB%8F%E6%89%8B%E5%86%8C-%E7%AC%AC6%E7%AF%87-%E5%B8%A6%E7%9D%80%E9%9D%A2%E8%AF%95%E9%A2%98%E5%AD%A6%E4%B9%A0%E7%BA%A2%E9%BB%91%E6%A0%91%E6%93%8D%E4%BD%9C%E5%8E%9F%E7%90%86-%E8%A7%A3%E6%9E%90%E4%BB%80%E4%B9%88%E6%97%B6%E5%80%99%E6%9F%93%E8%89%B2-%E6%80%8E%E4%B9%88%E8%BF%9B%E8%A1%8C%E6%97%8B%E8%BD%AC-%E4%B8%8E2-3%E6%A0%91%E6%9C%89%E4%BB%80%E4%B9%88%E5%85%B3%E8%81%94.html)
+7. [面经手册 · 第6篇《带着面试题学习红黑树操作原理，解析什么时候染色、怎么进行旋转、与2-3树有什么关联》](https://bugstack.cn/interview/2020/08/20/%E9%9D%A2%E7%BB%8F%E6%89%8B%E5%86%8C-%E7%AC%AC6%E7%AF%87-%E5%B8%A6%E7%9D%80%E9%9D%A2%E8%AF%95%E9%A2%98%E5%AD%A6%E4%B9%A0%E7%BA%A2%E9%BB%91%E6%A0%91%E6%93%8D%E4%BD%9C%E5%8E%9F%E7%90%86-%E8%A7%A3%E6%9E%90%E4%BB%80%E4%B9%88%E6%97%B6%E5%80%99%E6%9F%93%E8%89%B2-%E6%80%8E%E4%B9%88%E8%BF%9B%E8%A1%8C%E6%97%8B%E8%BD%AC-%E4%B8%8E2-3%E6%A0%91%E6%9C%89%E4%BB%80%E4%B9%88%E5%85%B3%E8%81%94.html)
+8. [面经手册 · 第7篇《ArrayList也这么多知识？一个指定位置插入就把谢飞机面晕了！》](https://bugstack.cn/interview/2020/08/27/%E9%9D%A2%E7%BB%8F%E6%89%8B%E5%86%8C-%E7%AC%AC7%E7%AF%87-ArrayList%E4%B9%9F%E8%BF%99%E4%B9%88%E5%A4%9A%E7%9F%A5%E8%AF%86-%E4%B8%80%E4%B8%AA%E6%8C%87%E5%AE%9A%E4%BD%8D%E7%BD%AE%E6%8F%92%E5%85%A5%E5%B0%B1%E6%8A%8A%E8%B0%A2%E9%A3%9E%E6%9C%BA%E9%9D%A2%E6%99%95%E4%BA%86.html)
diff --git a/interview-03/interview-03.iml b/interview-03/interview-03.iml
@@ -12,5 +12,7 @@
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />
     <orderEntry type="library" name="Maven: com.alibaba:fastjson:1.2.73" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: junit:junit:4.13" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.hamcrest:hamcrest-core:1.3" level="project" />
   </component>
 </module>
diff --git a/interview-05/src/main/java/T.java b/interview-05/src/main/java/T.java
@@ -0,0 +1,7 @@
+/**
+ * 博客：https://bugstack.cn - 沉淀、分享、成长，让自己和他人都能有所收获！
+ * 公众号：bugstack虫洞栈
+ * Create by 小傅哥(fustack) @2020
+ */
+public class T {
+}
diff --git a/interview-07/pom.xml b/interview-07/pom.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>interview</artifactId>
+        <groupId>org.itstack</groupId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>interview-07</artifactId>
+
+
+</project>
diff --git a/interview-07/src/test/java/org/itstack/interview/test/ApiTest.java b/interview-07/src/test/java/org/itstack/interview/test/ApiTest.java
@@ -0,0 +1,199 @@
+package org.itstack.interview.test;
+
+import com.alibaba.fastjson.JSON;
+import org.junit.Test;
+import sun.net.idn.Punycode;
+
+import javax.sound.midi.Soundbank;
+import java.lang.reflect.Array;
+import java.util.*;
+
+public class ApiTest {
+
+    public static void main(String[] args) {
+        List<String> list = new ArrayList<String>(Collections.nCopies(9, "a"));
+        System.out.println("初始化：" + list);
+
+        list.add(2, "b");
+        System.out.println("插入后：" + list);
+    }
+
+    @Test
+    public void t2() {
+        String[] strs = new String[10];
+        strs[5] = "1";
+
+        Arrays.asList();
+    }
+
+    @Test
+    public void test_remove() {
+        ArrayList<String> list = new ArrayList<String>();
+        list.add("a");
+        list.add("b");
+        list.add("c");
+        list.add("d");
+        list.add("e");
+        list.add("f");
+        list.add("g");
+        list.add("h");
+        list.add("i");
+        list.add("j");
+        System.out.println(list);
+
+        list.remove(2);
+
+        System.out.println(list);
+        System.out.println(list.size());
+    }
+
+    @Test
+    public void test_arraycopy() {
+        int[] oldArr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        int[] newArr = new int[oldArr.length + (oldArr.length >> 1)];
+
+        System.arraycopy(oldArr, 0, newArr, 0, oldArr.length);
+
+        newArr[11] = 11;
+        newArr[12] = 12;
+        newArr[13] = 13;
+        newArr[14] = 14;
+
+        System.out.println("数组元素：" + JSON.toJSONString(newArr));
+        System.out.println("数组长度：" + newArr.length);
+
+        /**
+         * 测试结果
+         *
+         * 数组元素：[1,2,3,4,5,6,7,8,9,10,0,11,12,13,14]
+         * 数组长度：15
+         */
+    }
+
+    @Test
+    public void test_copy_remove() {
+        int[] oldArr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+
+        int index = 2;
+        int numMoved = 10 - index - 1;
+
+        System.arraycopy(oldArr, index + 1, oldArr, index, numMoved);
+
+        System.out.println("数组元素：" + JSON.toJSONString(oldArr));
+    }
+
+    @Test
+    public void init_01() {
+        ArrayList<String> list = new ArrayList<String>();
+        list.add("aaa");
+        list.add("bbb");
+        list.add("ccc");
+    }
+
+    @Test
+    public void init_02() {
+
+        List<String> list = Arrays.asList("aaa", "bbb", "ccc");
+        list.add("ddd");
+
+        ArrayList<String> obj = new ArrayList<String>(Arrays.asList("aaa", "bbb", "ccc"));
+
+    }
+
+    @Test
+    public void init_03() {
+        ArrayList<String> list = new ArrayList<String>() {{
+            add("aaa");
+            add("bbb");
+            add("ccc");
+        }};
+    }
+
+    @Test
+    public void init_04() {
+        ArrayList<Integer> list = new ArrayList<Integer>(Collections.nCopies(10, 0));
+    }
+
+    @Test
+    public void t() {
+        List<Integer> list1 = Arrays.asList(1, 2, 3);
+        System.out.println("通过数组转换：" + (list1.toArray().getClass() == Object[].class));
+
+        ArrayList<Integer> list2 = new ArrayList<Integer>(Arrays.asList(1, 2, 3));
+        System.out.println("通过集合转换：" + (list2.toArray().getClass() == Object[].class));
+    }
+
+
+    @Test
+    public void t_hashIdx() {
+
+        List<String> list = new ArrayList<String>(Collections.<String>nCopies(8, "0"));
+
+        list.set("a".hashCode() & 8 - 1, "a");
+        list.set("b".hashCode() & 8 - 1, "b");
+        list.set("c".hashCode() & 8 - 1, "c");
+        list.set("d".hashCode() & 8 - 1, "d");
+        list.set("e".hashCode() & 8 - 1, "e");
+        list.set("f".hashCode() & 8 - 1, "f");
+        list.set("g".hashCode() & 8 - 1, "g");
+
+        System.out.println("元素集合:" + list);
+
+        System.out.println("获取元素f [\"f\".hashCode() & 8 - 1)] Idx：" + ("f".hashCode() & (8 - 1)) + " 元素：" + list.get("f".hashCode() & 8 - 1));
+        System.out.println("获取元素e [\"e\".hashCode() & 8 - 1)] Idx：" + ("e".hashCode() & (8 - 1)) + " 元素：" + list.get("e".hashCode() & 8 - 1));
+        System.out.println("获取元素d [\"d\".hashCode() & 8 - 1)] Idx：" + ("d".hashCode() & (8 - 1)) + " 元素：" + list.get("d".hashCode() & 8 - 1));
+    }
+
+    @Test
+    public void t_ensureCapacity01(){
+        final int N = 10000000;
+        ArrayList<Integer> list = new ArrayList<Integer>();
+        long startTime = System.currentTimeMillis();
+        for (int i = 0; i < N; i++) {
+            list.add(i);
+        }
+        System.out.println("默认情况耗时："+(System.currentTimeMillis() - startTime));
+    }
+
+    @Test
+    public void t_ensureCapacity02(){
+        final int N = 10000000;
+        ArrayList<Integer> list = new ArrayList<Integer>(N);
+        long startTime = System.currentTimeMillis();
+        for (int i = 0; i < N; i++) {
+            list.add(i);
+        }
+        System.out.println("初始定长容量耗时："+(System.currentTimeMillis() - startTime));
+    }
+
+    @Test
+    public void t_ensureCapacity03(){
+        final int N = 10000000;
+        ArrayList<Object> list = new ArrayList<Object>();
+        long startTime = System.currentTimeMillis();
+        list.ensureCapacity(N);
+        for (int i = 0; i < N; i++) {
+            list.add(i);
+        }
+        System.out.println("使用ensureCapacity方法耗时："+(System.currentTimeMillis() - startTime));
+    }
+
+    @Test
+    public void tt(){
+        ArrayList<Object> list = new ArrayList<Object>();
+        final int N = 10000000;
+        for (int i = 0; i < N; i++) {
+            list.add(i);
+        }
+
+        ArrayList<Object> list2 = new ArrayList<Object>();
+        long startTime1 = System.currentTimeMillis();
+//        list2.ensureCapacity(N);
+        for (int i = 0; i < N; i++) {
+            list2.add(i);
+        }
+        long endTime1 = System.currentTimeMillis();
+        System.out.println("使用ensureCapacity方法后："+(endTime1 - startTime1));
+    }
+
+}
diff --git a/pom.xml b/pom.xml
@@ -14,6 +14,7 @@
         <module>interview-03</module>
         <module>interview-04</module>
         <module>interview-05</module>
+        <module>interview-07</module>
     </modules>
 
     <dependencies>
@@ -22,6 +23,13 @@
             <artifactId>fastjson</artifactId>
             <version>1.2.73</version>
         </dependency>
+        <!-- https://mvnrepository.com/artifact/junit/junit -->
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.13</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>