diff --git a/com/study/demo/Demo.java b/com/study/demo/Demo.java
new file mode 100644
index 0000000..cd317cd
--- /dev/null
+++ b/com/study/demo/Demo.java
@@ -0,0 +1,7 @@
+package com.study.demo;
+
+public class Demo {
+	public static void main(String [] args) {
+		System.out.println("HelloWorld!");
+		}
+}
diff --git a/com/study/demo/test1_1.java b/com/study/demo/test1_1.java
new file mode 100644
index 0000000..5f0e51d
--- /dev/null
+++ b/com/study/demo/test1_1.java
@@ -0,0 +1,13 @@
+package com.study.demo;
+import java.util.Scanner;
+// I am 212306206
+public class test1_type {
+	public static void main(String[] args) {
+		Scanner scanner = new Scanner (System.in);
+		int a = scanner.nextInt();
+		int b = scanner.nextInt();
+		int sum = a + b;
+		System.out.println(a + " + " + b + " = " + sum);
+		scanner.close();
+	}
+}
diff --git a/com/study/demo/test1_2.java b/com/study/demo/test1_2.java
new file mode 100644
index 0000000..31d5ee0
--- /dev/null
+++ b/com/study/demo/test1_2.java
@@ -0,0 +1,16 @@
+package com.study.demo;
+
+public class test2_for {
+    public static void main(String[] args) {
+        int[] numbers = new int[5];
+        for (int i = 0; i < numbers.length; i++) {
+            numbers[i] = i * 10;
+        }
+
+        System.out.print("数组内容: ");
+        for (int i = 0; i < numbers.length; i++) {
+            System.out.print(numbers[i] + " ");
+        }
+    }
+}
+
diff --git a/com/study/demo/test1_3.java b/com/study/demo/test1_3.java
new file mode 100644
index 0000000..05189ee
--- /dev/null
+++ b/com/study/demo/test1_3.java
@@ -0,0 +1,19 @@
+package com.study.demo;
+
+public class test3_1_99 {
+    public static void main(String[] args) {
+        int[] numbers = new int[99];
+
+        for (int i = 0; i < numbers.length; i++) {
+            numbers[i] = i + 1;
+        }
+
+        int sum = 0;
+        for (int i = 0; i < numbers.length; i++) {
+            sum += numbers[i];
+        }
+
+        System.out.println("1+2+...+99 的和 = " + sum);
+    }
+}
+
diff --git a/com/study/demo/test2_1.java b/com/study/demo/test2_1.java
new file mode 100644
index 0000000..bf44c29
--- /dev/null
+++ b/com/study/demo/test2_1.java
@@ -0,0 +1,14 @@
+package com.study.demo; 
+import java.util.Scanner;
+
+public class test4 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        double r1 = sc.nextDouble();
+        double r2 = sc.nextDouble();
+        sc.close();
+
+        double R = 1 / (1 / r1 + 1 / r2);
+        System.out.printf("%.2f\n", R);
+    }
+}
diff --git a/com/study/demo/test2_2.java b/com/study/demo/test2_2.java
new file mode 100644
index 0000000..f3b570f
--- /dev/null
+++ b/com/study/demo/test2_2.java
@@ -0,0 +1,14 @@
+package com.study.demo;
+import java.util.Scanner;
+
+public class test5 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int a = scanner.nextInt();
+        int b = scanner.nextInt();
+        int c = scanner.nextInt();
+        double pi = 3.1415926535;
+        double area = a * b * c + a * c + (pi * c * c) / 4;
+        System.out.printf("%.3f\n", area / 10000);
+    }
+}
\ No newline at end of file
diff --git a/com/study/demo/test2_3.java b/com/study/demo/test2_3.java
new file mode 100644
index 0000000..f1ae9e3
--- /dev/null
+++ b/com/study/demo/test2_3.java
@@ -0,0 +1,12 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test6 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int result = 1 << n;
+        System.out.println(result);
+    }
+}
\ No newline at end of file
diff --git a/com/study/demo/test2_4.java b/com/study/demo/test2_4.java
new file mode 100644
index 0000000..0f0ced7
--- /dev/null
+++ b/com/study/demo/test2_4.java
@@ -0,0 +1,14 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test7 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int x = scanner.nextInt();
+        int y = scanner.nextInt();
+        int startYear = 2016, startMonth = 8;
+        int totalMonths = (x - startYear) * 12 + y - startMonth + 1;
+        System.out.println(totalMonths);
+    }
+}
\ No newline at end of file
diff --git a/com/study/demo/test2_5.java b/com/study/demo/test2_5.java
new file mode 100644
index 0000000..87d354a
--- /dev/null
+++ b/com/study/demo/test2_5.java
@@ -0,0 +1,19 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test8 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int x = scanner.nextInt();
+        int k = scanner.nextInt();
+        int a = x / 1000 % k;
+        int b = x / 100 % 10 % k;
+        int c = x / 10 % 10 % k;
+        int d = x % 10 % k;
+        System.out.print(a);
+        System.out.print(b);
+        System.out.print(c);
+        System.out.println(d);
+    }
+}
diff --git a/com/study/demo/test3_1.class b/com/study/demo/test3_1.class
new file mode 100644
index 0000000..8a09b03
Binary files /dev/null and b/com/study/demo/test3_1.class differ
diff --git a/com/study/demo/test3_1.java b/com/study/demo/test3_1.java
new file mode 100644
index 0000000..ef5f27b
--- /dev/null
+++ b/com/study/demo/test3_1.java
@@ -0,0 +1,22 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test3_1 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int[] arr = new int[n];
+        for (int i = 0; i < n; i++) {
+            arr[i] = scanner.nextInt();
+        }
+        for (int i = 0; i < n / 2; i++) {
+            int temp = arr[i];
+            arr[i] = arr[n - 1 - i];
+            arr[n - 1 - i] = temp;
+        }
+        for (int i = 0; i < n; i++) {
+            System.out.print(arr[i] + (i == n - 1 ? "" : " "));
+        }
+    }
+}
diff --git a/com/study/demo/test3_2.class b/com/study/demo/test3_2.class
new file mode 100644
index 0000000..5ba259a
Binary files /dev/null and b/com/study/demo/test3_2.class differ
diff --git a/com/study/demo/test3_2.java b/com/study/demo/test3_2.java
new file mode 100644
index 0000000..6c23487
--- /dev/null
+++ b/com/study/demo/test3_2.java
@@ -0,0 +1,23 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test3_2 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int[] a = new int[n];
+        int[] b = new int[n];
+        for (int i = 0; i < n; i++) {
+            a[i] = scanner.nextInt();
+        }
+        for (int i = 0; i < n; i++) {
+            b[i] = scanner.nextInt();
+        }
+        int sum = 0;
+        for (int i = 0; i < n; i++) {
+            sum += a[i] * b[i];
+        }
+        System.out.println(sum);
+    }
+}
diff --git a/com/study/demo/test3_3.class b/com/study/demo/test3_3.class
new file mode 100644
index 0000000..0f74550
Binary files /dev/null and b/com/study/demo/test3_3.class differ
diff --git a/com/study/demo/test3_3.java b/com/study/demo/test3_3.java
new file mode 100644
index 0000000..1b1d23b
--- /dev/null
+++ b/com/study/demo/test3_3.java
@@ -0,0 +1,25 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test3_3 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int[] arr = new int[n];
+        for (int i = 0; i < n; i++) {
+            arr[i] = scanner.nextInt();
+        }
+        int maxLen = 1, currentLen = 1;
+        for (int i = 1; i < n; i++) {
+            if (arr[i] == arr[i - 1]) {
+                currentLen++;
+            } else {
+                maxLen = Math.max(maxLen, currentLen);
+                currentLen = 1;
+            }
+        }
+        maxLen = Math.max(maxLen, currentLen);
+        System.out.println(maxLen);
+    }
+}
diff --git a/com/study/demo/test3_4.class b/com/study/demo/test3_4.class
new file mode 100644
index 0000000..04b1e71
Binary files /dev/null and b/com/study/demo/test3_4.class differ
diff --git a/com/study/demo/test3_4.java b/com/study/demo/test3_4.java
new file mode 100644
index 0000000..63d2a91
--- /dev/null
+++ b/com/study/demo/test3_4.java
@@ -0,0 +1,23 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test3_4 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int m = scanner.nextInt();
+        int[][] image = new int[n][m];
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                image[i][j] = scanner.nextInt();
+            }
+        }
+        for (int j = 0; j < m; j++) {
+            for (int i = n - 1; i >= 0; i--) {
+                System.out.print(image[i][j] + (i == 0 ? "" : " "));
+            }
+            System.out.println();
+        }
+    }
+}
diff --git a/com/study/demo/test3_5.class b/com/study/demo/test3_5.class
new file mode 100644
index 0000000..596c796
Binary files /dev/null and b/com/study/demo/test3_5.class differ
diff --git a/com/study/demo/test3_5.java b/com/study/demo/test3_5.java
new file mode 100644
index 0000000..574959b
--- /dev/null
+++ b/com/study/demo/test3_5.java
@@ -0,0 +1,34 @@
+package com.study.demo;
+
+import java.util.Scanner;
+
+public class test3_5 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int[] t = new int[n - 1];
+        int[] s = new int[n];
+        for (int i = 0; i < n - 1; i++) {
+            t[i] = scanner.nextInt();
+        }
+        for (int i = 0; i < n; i++) {
+            s[i] = scanner.nextInt();
+        }
+        int x = scanner.nextInt();
+        int y = scanner.nextInt();
+
+        int total = 0;
+        if (x < y) {
+            for (int i = x - 1; i < y - 1; i++) {
+                total += s[i] + t[i];
+            }
+            total += s[y - 1];
+        } else {
+            for (int i = x - 1; i >= y; i--) {
+                total += s[i] + (i > 0 ? t[i - 1] : 0);
+            }
+            total += s[y - 1];
+        }
+        System.out.println(total);
+    }
+}
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..3d8d012
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1759070547,
+        "narHash": "sha256-JVZl8NaVRYb0+381nl7LvPE+A774/dRpif01FKLrYFQ=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "647e5c14cbd5067f44ac86b74f014962df460840",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..3ca1e3b
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,21 @@
+{
+  description = "A Nix-flake-based development environment";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  outputs = { self, nixpkgs }:
+  let
+    supportedSystems = [ "x86_64-linux" "aarch64-linux" ];
+    forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+      pkgs = import nixpkgs { inherit self system; };
+    });
+  in
+  {
+    devShells = forEachSupportedSystem ({ pkgs }: {
+      default = pkgs.mkShell {
+        packages = with pkgs; [
+          jdk8
+        ];
+      };
+    });
+  };
+}
+