singleton design pattern

Author: hansiming

src/com/cszjo/design/patterns/factory/singleton/DoubleCheckSingleton.java

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+package com.cszjo.design.patterns.factory.singleton;
+
+/**
+ * Created by hansiming on 2017/10/19.
+ */
+public class DoubleCheckSingleton {
+
+    private static DoubleCheckSingleton instance = null;
+
+    private DoubleCheckSingleton() {
+        // prevent instance on outer
+    }
+
+    public static DoubleCheckSingleton getInstance() {
+        if (instance == null) {
+            synchronized (DoubleCheckSingleton.class) {
+                if (instance == null) {
+                    instance = new DoubleCheckSingleton();
+                }
+            }
+        }
+        return instance;
+    }
+}

src/com/cszjo/design/patterns/factory/singleton/StaticHolderSingleton.java

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+package com.cszjo.design.patterns.factory.singleton;
+
+/**
+ * Created by hansiming on 2017/10/19.
+ */
+public class StaticHolderSingleton {
+
+    private static class SingletonHolder {
+        private final static StaticHolderSingleton instance = new StaticHolderSingleton();
+    }
+
+    public static StaticHolderSingleton getInstance() {
+        return SingletonHolder.instance;
+    }
+}

src/com/cszjo/offer/Demo10.java

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+package com.cszjo.offer;
+
+/**
+ * 依旧是斐波拉契数列
+ * 我们可以用2*1的小矩形横着或者竖着去覆盖更大的矩形。
+ * 请问用n个2*1的小矩形无重叠地覆盖一个2*n的大矩形，总共有多少种方法？
+ * Created by hansiming on 2017/10/19.
+ */
+public class Demo10 {
+
+    public int RectCover(int target) {
+        if (target <= 2)
+            return target;
+
+        return RectCover(target - 1) + RectCover(target - 2);
+    }
+}

src/com/cszjo/offer/Demo11.java

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+package com.cszjo.offer;
+
+/**
+ * 输入一个整数，输出该数二进制表示中1的个数。其中负数用补码表示。
+ * Created by hansiming on 2017/10/19.
+ */
+public class Demo11 {
+
+    public int NumberOf1(int n) {
+
+        int count = 0;
+        if (n < 0) {
+            n = n & 0x7FFFFFFF;
+            count ++;
+        }
+
+        while (n > 0) {
+            count += n & 1;
+            n = n >> 1;
+        }
+
+        return count;
+    }
+}

src/com/cszjo/offer/Demo9.java

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+package com.cszjo.offer;
+
+/**
+ * 一只青蛙一次可以跳上1级台阶，也可以跳上2级……它也可以跳上n级。
+ * 求该青蛙跳上一个n级的台阶总共有多少种跳法。
+ * Created by hansiming on 2017/10/19.
+ */
+public class Demo9 {
+
+    public int JumpFloorII(int target) {
+
+        if (target <= 2)
+            return target;
+
+        return 2 * JumpFloorII(target - 1);
+    }
+}