彭晖=Java培训-数组

src/main/java/com/exercise/eighth/ExerciseFifth.java

+package com.exercise.eighth;
+
+import java.util.Arrays;
+
+/**
+ * 4.写一段代码，实现System.arraycopy方法的功能
+ * @author elliot
+ */
+public class ExerciseFifth {
+    public static void main(String[] args) {
+        int[] nums = {1, 2, 3, 4, 5, 6};
+        int[] newNums = new int[10];
+        arraycopy(nums, 1, newNums, 2, 3);
+
+        System.out.println(Arrays.toString(newNums));
+    }
+
+    private static void arraycopy(Object[] src, int srcPos, Object[] dest, int destPos, int length) {
+        for (int i = 0; i < length; i++) {
+            dest[destPos++] = src[srcPos++];
+        }
+    }
+
+    private static void arraycopy(float[] src, int srcPos, float[] dest, int destPos, int length) {
+        for (int i = 0; i < length; i++) {
+            dest[destPos++] = src[srcPos++];
+        }
+    }
+
+    private static void arraycopy(double[] src, int srcPos, double[] dest, int destPos, int length) {
+        for (int i = 0; i < length; i++) {
+            dest[destPos++] = src[srcPos++];
+        }
+    }
+
+    private static void arraycopy(int[] src, int srcPos, int[] dest, int destPos, int length) {
+        for (int i = 0; i < length; i++) {
+            dest[destPos++] = src[srcPos++];
+        }
+    }
+}

src/main/java/com/exercise/eighth/ExerciseFirst.java

+package com.exercise.eighth;
+
+/**
+ * 彭晖=Java培训-数组
+ * .定义一个数组，其中元素为公司的一级部门名称，按照【下标:值】
+ * 格式打印出来。
+ * 如：0:xxx, 1:xxx, 2:xxx
+ * @author elliot
+ */
+public class ExerciseFirst {
+    public static void main(String[] args) {
+        String[] company = {"内部服务中心", "客户成功中心", "市场中心", "技术中心", "产品中心"};
+        for(int i=0; i < company.length; i++){
+            System.out.println(i+":"+company[i]);
+        }
+    }
+}

src/main/java/com/exercise/eighth/ExerciseFourth.java

+package com.exercise.eighth;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 统计数组【1，5，6，12，1，32，5，6】中每个元素出现的次数
+ * @author elliot
+ */
+public class ExerciseFourth {
+    public static void main(String[] args) {
+        int[] nums = {1, 5, 6, 12, 1, 32, 5, 6};
+        System.out.println(counter(nums).toString());
+    }
+
+    private static Map<Integer, Integer> counter(int[] array) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int element: array) {
+            map.put(element, map.getOrDefault(element, 0) + 1);
+        }
+        return map;
+    }
+}

src/main/java/com/exercise/eighth/ExerciseSecond.java

+package com.exercise.eighth;
+
+import java.util.Arrays;
+
+/**
+ * 将int数组【99、23、34、67、123、234、1、98】按照升序排列
+ * @author elliot
+ */
+public class ExerciseSecond {
+    public static void main(String[] args) {
+        int[] nums = {99, 23, 34, 67, 123, 234, 1, 98};
+        Arrays.sort(nums);
+        System.out.println(Arrays.toString(nums));
+    }
+}

src/main/java/com/exercise/eighth/ExerciseThird.java

+package com.exercise.eighth;
+
+import java.util.*;
+
+/**
+ * 去掉数组【1、2、3、4、2、2、1、5、6】中的重复元素
+ * @author elliot
+ */
+public class ExerciseThird {
+    public static void main(String[] args) {
+        int[] nums = {1, 2, 3, 4, 2, 2, 1, 5, 6};
+
+        int[] news = intsUnique(nums);
+        System.out.println(Arrays.toString(news));;
+    }
+    /**
+     * int[] 数组去重
+     * @param arr
+     * @return
+     */
+    public static int[] intsUnique(int[] arr){
+        int[] news = new int[getNoRepeatNum(arr)];
+
+        int index = 0;
+        for (int i = 0; i < arr.length; i++) {
+            if(Arrays.binarySearch(news, arr[i]) < 0){
+                news[index] = arr[i];
+                index ++;
+            }
+        }
+        return news;
+    }
+
+    /**
+     * 去重后的元素个数
+     * @param ints
+     * @return
+     */
+    public static int getNoRepeatNum(int[] ints) {
+        List list = new ArrayList();
+        for(int i=0; i<ints.length; i++){
+            if(!list.contains(ints[i])){
+                list.add(ints[i]);
+            }
+        }
+        return list.size();
+    }
+}