diff --git a/src/singleton/Singleton6.java b/src/singleton/Singleton6.java
index c864a53..4dfd85e 100644
--- a/src/singleton/Singleton6.java
+++ b/src/singleton/Singleton6.java
@@ -5,7 +5,7 @@ package singleton;
  * 虽然达到了按需初始化的目的, 同步代码块
  * */
 public class Singleton6 {
-    private static Singleton6 INSTANCE;
+    private static volatile Singleton6 INSTANCE;
 
     private Singleton6() {
     }
diff --git a/src/strategy/Cat.java b/src/strategy/Cat.java
new file mode 100644
index 0000000..b61b379
--- /dev/null
+++ b/src/strategy/Cat.java
@@ -0,0 +1,26 @@
+package strategy;
+
+public class Cat implements Comparable<Cat>{
+    private int weight;
+    private int height;
+
+    public Cat(int weight, int height) {
+        this.weight = weight;
+        this.height = height;
+    }
+
+    @Override
+    public String toString() {
+        return "Cat{" +
+                "weight=" + weight +
+                ", height=" + height +
+                '}';
+    }
+
+    @Override
+    public int compareTo(Cat c) {
+        if(this.weight < c.weight) return -1;
+        else if(this.weight > c.weight) return 1;
+        else return 0;
+    }
+}
diff --git a/src/strategy/CatHeightComparator.java b/src/strategy/CatHeightComparator.java
new file mode 100644
index 0000000..dd2cf5e
--- /dev/null
+++ b/src/strategy/CatHeightComparator.java
@@ -0,0 +1,8 @@
+package strategy;
+
+public class CatHeightComparator implements Comparator<Cat>{
+    @Override
+    public int compareTo(Cat t1, Cat t2) {
+        return 0;
+    }
+}
diff --git a/src/strategy/CatWeightComparator.java b/src/strategy/CatWeightComparator.java
new file mode 100644
index 0000000..2095afe
--- /dev/null
+++ b/src/strategy/CatWeightComparator.java
@@ -0,0 +1,8 @@
+package strategy;
+
+public class CatWeightComparator implements Comparator<Cat>{
+    @Override
+    public int compareTo(Cat t1, Cat t2) {
+        return 0;
+    }
+}
diff --git a/src/strategy/Comparator.java b/src/strategy/Comparator.java
new file mode 100644
index 0000000..ef12012
--- /dev/null
+++ b/src/strategy/Comparator.java
@@ -0,0 +1,5 @@
+package strategy;
+
+public interface Comparator<T> {
+    int compareTo(T t1, T t2);
+}
diff --git a/src/strategy/Dog.java b/src/strategy/Dog.java
new file mode 100644
index 0000000..e0d10e8
--- /dev/null
+++ b/src/strategy/Dog.java
@@ -0,0 +1,23 @@
+package strategy;
+
+public class Dog implements Comparable<Dog>{
+    int food;
+
+    public Dog(int food) {
+        this.food = food;
+    }
+
+    @Override
+    public String toString() {
+        return "Dog{" +
+                "food=" + food +
+                '}';
+    }
+
+    @Override
+    public int compareTo(Dog d) {
+        if(this.food < d.food) return -1;
+        else if(this.food > d.food) return 1;
+        else return 0;
+    }
+}
diff --git a/src/strategy/DogComparator.java b/src/strategy/DogComparator.java
new file mode 100644
index 0000000..8df7845
--- /dev/null
+++ b/src/strategy/DogComparator.java
@@ -0,0 +1,10 @@
+package strategy;
+
+public class DogComparator implements Comparator<Dog>{
+    @Override
+    public int compareTo(Dog d1, Dog d2) {
+        if(d1.food < d2.food) return -1;
+        else if(d1.food > d2.food) return 1;
+        else return 0;
+    }
+}
diff --git a/src/strategy/Sorter.java b/src/strategy/Sorter.java
new file mode 100644
index 0000000..3fc1a05
--- /dev/null
+++ b/src/strategy/Sorter.java
@@ -0,0 +1,29 @@
+package strategy;
+
+import java.util.Arrays;
+
+public class Sorter<T> {
+     public void sort(T[] arr, Comparator<T> comparator){
+          for (int i = 0; i < arr.length - 1; i++) {
+               int minPos = i;
+               for (int j = i+1; j < arr.length; j++) {
+                    minPos = comparator.compareTo(arr[j], arr[minPos]) == -1 ? j : minPos;
+               }
+               swap(arr, i, minPos);
+          }
+     }
+
+     private void swap(T[] arr, int i, int minPos) {
+          T temp = arr[i];
+          arr[i] = arr[minPos];
+          arr[minPos] = temp;
+     }
+
+     public static void main(String[] args) {
+          Dog[] dogs = new Dog[]{new Dog(5), new Dog(1), new Dog(6)};
+          Cat[] cats = new Cat[]{new Cat(6,2), new Cat(3,4), new Cat(5,5)};
+          Sorter<Dog> sorter = new Sorter<>();
+          sorter.sort(dogs, new DogComparator());
+          System.out.println(Arrays.toString(dogs));
+     }
+}