给静态工具类添加私有构造器，防止实例化和继承。

shengshijun · shengshijun · commit ed7cb3723dfa · 2015-02-28T20:41:39.000+08:00
diff --git a/src/main/java/ssj/algorithm/ArrayUtil.java b/src/main/java/ssj/algorithm/ArrayUtil.java
@@ -17,6 +17,8 @@
  * Created by shenshijun on 14-12-20.
  */
 public class ArrayUtil {
+    private ArrayUtil() {
+    }
 
     public static <T> void swap(T[] array, int left, int right) {
         Preconditions.checkNotNull(array);
diff --git a/src/main/java/ssj/algorithm/math/BitUtil.java b/src/main/java/ssj/algorithm/math/BitUtil.java
@@ -6,6 +6,10 @@
  * Created by shenshijun on 15/2/10.
  */
 public class BitUtil {
+
+    private BitUtil() {
+    }
+
     public static boolean testBit(long value, int index) {
         Preconditions.checkArgument(index >= 0 && index < Long.SIZE);
         return (value & (1L << index)) != 0;
diff --git a/src/main/java/ssj/algorithm/math/MathUtil.java b/src/main/java/ssj/algorithm/math/MathUtil.java
@@ -11,6 +11,10 @@
  * Created by shenshijun on 14-12-21.
  */
 public class MathUtil {
+    private MathUtil() {
+
+    }
+
     private static Random randor = new Random();
 
     public static int gcd(int a, int b) {
diff --git a/src/main/java/ssj/algorithm/matrix/MatrixUtil.java b/src/main/java/ssj/algorithm/matrix/MatrixUtil.java
@@ -11,6 +11,10 @@
  * Created by shenshijun on 15/2/2.
  */
 public class MatrixUtil {
+    private MatrixUtil() {
+
+    }
+
     /**
      * 原理
      * 1            *      2                   *      1
diff --git a/src/main/java/ssj/algorithm/string/StringUntil.java b/src/main/java/ssj/algorithm/string/StringUntil.java
@@ -13,6 +13,9 @@
  * Created by shenshijun on 15/2/1.
  */
 public class StringUntil {
+    private StringUntil() {
+    }
+
     /**
      * 比较两个字符串的中的字符是否完全不同
      * 使用数组和BitSet都可以实现，但是BitSet好管理一点。
