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, 43 insertions, 0 deletions

diff --git a/java/code/ComplexCalculations.java b/java/code/ComplexCalculations.java
new file mode 100644
index 0000000..5ce056f
--- /dev/null
+++ b/java/code/ComplexCalculations.java
@@ -0,0 +1,43 @@
+import java.util.Scanner;
+import java.util.InputMismatchException;
+
+class Complex {
+    double real, imag;
+    Complex(double r, double i) {
+        real = r;
+        imag = i;
+    }
+    @Override
+    public String toString() {
+        return real + (imag > 0.0 ? " + " : " - ") + Math.abs(imag) + "i";
+    }
+}
+
+class ComplexOperations {
+    static Complex add(Complex a, Complex b) {
+        return new Complex(a.real + b.real, a.imag + b.imag);
+    }
+}
+
+class ComplexCalculations {
+    static Complex takeComplexInput() {
+        var sc = new Scanner(System.in);
+        System.out.print("  Enter real part: ");
+        var real = sc.nextDouble();
+        System.out.print("  Enter imaginary part: ");
+        var imaginary = sc.nextDouble();
+        return new Complex(real, imaginary);
+    }
+    public static void main(String args[]) {
+        try {
+            System.out.println("First complex number:-");
+            var x = takeComplexInput();
+            System.out.println("Second complex number:-");
+            var y = takeComplexInput();
+            System.out.println("(" + x + ") + (" + y + ") = " + ComplexOperations.add(x, y));
+        } catch (InputMismatchException e) {
+            System.err.println("Invalid number given as input");
+        }
+    }
+}
+