Add Java assignments to the repository

.gitignore: The build files, files left by editors like *~ and the PDF
documents for the assignments are to be ignored for the purposes of
version control.

README.rst: Rewrite, with one line description in Chinese.

java/alist.txt: List of assignments, sorted in the order of the list of
assignments, with the ones with completed documentation marked with `#`.

java/buildall: Script that will build all of the assignments into one
PDF file; to be rehauled for the final document.

code/*.java: The Java source code for the assignments.

dbld: Script that builds a PDF document for a single assignment.

index.typ: The list of assignments, subject to update for further
refinement and inclusion of yet more assignments.

jbld: Script that compiles code for a single Java assignment.

output/*.typ: Typst file containing the output (sessions) obtained from
running the individual Java assignments.

state.sql: Future alternative to `alist.txt`, under development.

template.typ: The Typst template used across all of assignment,
containing common code for the uniform styling, such as page border.

text/*.typ: Typst file documenting each Java assignment.

vendor/Java.sublime-syntax: Updated Sublime Text syntax file for Java,
used for newer syntax features, such as `var`, not yet available in
syntaxes shipped with Typst.

vendor/gr.tmTheme: A grayscale TextMate theme to be used for code in the
documents generated by Typst suitable for black and white printing.

wltd: Difference between the files in `code/` and `text/`, and `code/`
and `output`; need to be rewritten along with `state.sql`.

1 files changed, 112 insertions, 0 deletions

diff --git a/java/code/StringOperations.java b/java/code/StringOperations.java
new file mode 100644
index 0000000..de817ce
--- /dev/null
+++ b/java/code/StringOperations.java
@@ -0,0 +1,112 @@
+import java.util.Scanner;
+
+class MyString {
+    String str;
+
+    MyString(String s) { str = s; }
+
+    String valueOf() { return str; }
+
+    int countWords() {
+        int count = 0, size = str.length();
+        enum state { WORD, SPACE };
+        state st = state.WORD;
+        for (int i = 0; i < size; i++) {
+            char c = str.charAt(i);
+            if (c == ' ' || c == '\t' || c == '\n' || c == '\r') {
+                st = state.SPACE;
+            } else if (st != state.WORD) {
+                st = state.WORD;
+                count++;
+            }
+        }
+        return count;
+    }
+
+    MyString reverse() {
+        char[] arr = str.toCharArray();
+        int end = arr.length - 1;
+        for (int i = 0; i < arr.length / 2; i++, end--) {
+            char tmp = arr[i];
+            arr[i] = arr[end];
+            arr[end] = tmp;
+        }
+        return new MyString(String.copyValueOf(arr));
+    }
+    
+    MyString toLowerCase() {
+        char[] arr = str.toCharArray();
+        char[] narr = new char[arr.length];
+        for (int i = 0; i < arr.length; i++) {
+            char c = arr[i];
+            if ('A' <= c && c <= 'Z') c += 'a' - 'A';
+            narr[i] = c;
+        }
+        return new MyString(String.copyValueOf(narr));
+    }
+    
+    boolean equals(MyString ms) {
+        char[] arr1 = str.toCharArray();
+        char[] arr2 = ms.valueOf().toCharArray();
+        if (arr1.length != arr2.length) return false;
+        for (int i = 0; i < arr1.length; i++) {
+            if (arr1[i] != arr2[i]) return false;
+        }
+        return true;
+    }
+
+    boolean isCaseInsensitivePalindrome() {
+        return str.toLowerCase().equals(reverse().toLowerCase().valueOf());
+    }
+}
+
+class StringOperations {
+    static void menu() {
+        System.out.println(
+            "Options:\n" +
+            " 1. Re-enter a string\n" +
+            " 2. Display the string\n" +
+            " 3. Count words in the string\n" +
+            " 4. Reverse the string\n" +
+            " 5. Case-insensitively check whether the string is palindrome or not\n" +
+            " 6. Exit\n");
+    }
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Menu-driven program for string operations");
+        System.out.print("Enter a string: ");
+        MyString ms = new MyString(sc.nextLine());
+        while (true) {
+            menu();
+            System.out.print("Enter your choice: ");
+            int choice = sc.nextInt();
+            sc.skip("\n");
+            switch (choice) {
+            case 1:
+                System.out.print("Enter a string: ");
+                ms = new MyString(sc.nextLine());
+                break;
+            case 2:
+                System.out.println("The string is: " + ms.valueOf());
+                break;
+            case 3:
+                int count = ms.countWords();
+                System.out.println("The string has " + count + " words.");
+                break;
+            case 4:
+                System.out.println("The given string reversed is: " + ms.reverse().valueOf());
+                break;
+            case 5:
+                System.out.println("The given string is" +
+                        (ms.isCaseInsensitivePalindrome() ? "" : "n't") +
+                        " case-insensitively palindrome.");
+                break;
+            case 6:
+                System.out.println("Bye.");
+                return;
+            default:
+                System.out.println("Invalid choice, try again.");
+            }
+        }
+    }
+}