Add String challenges from other PR + flags for turning on and off `v…

…oid main` (Together-Java#18)

* Update division.md

* Add basic feature flags impl

* Integrate String challenges

Fix script to not make an out.json

Co-Authored-By: alphaBEE <[email protected]>

* Remove "float point"

* Fix mdlint complaints

---------

Co-authored-by: alphaBEE <[email protected]>

book.toml

@@ -8,4 +8,13 @@ multilingual = false
 [output.html]
 git-repository-url = "https://github.com/Together-Java/ModernJava"
 edit-url-template = "https://github.com/Together-Java/ModernJava/edit/develop/{path}"
-mathjax-support = true
+mathjax-support = true
+
+[preprocessor.features]
+command = "python3 features.py"
+# Not ready
+toplevel_anonymous_class = true
+# Not ready
+simple_io = true
+# Turn on when Java 21 released
+java_21 = false

features.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python3
+
+import json
+import sys
+
+def preprocess_content(context, content):
+    options = context.get("config", {}).get("preprocessor", {}).get("features", {})
+    newContent = []
+    skipping = False
+    for line in content.splitlines():
+        if skipping:
+            if line.strip() == "~ENDIF" or line.strip() == "~ ENDIF":
+                skipping = False
+            elif line.strip() == "~ELSE" or line.strip() == "~ ELSE":
+                skipping = False
+        elif line.strip().startswith("~IF ") or line.strip().startswith("~ IF "):
+            if not options.get(line.split(" ", 2)[1].strip(), False):
+                skipping = True
+        elif line.strip() == "~ENDIF" or line.strip() == "~ ENDIF":
+            continue
+        elif line.strip() == "~ELSE" or line.strip() == "~ ELSE":
+            skipping = True
+            continue
+        else:
+            if options.get("simple_io", False) and options.get("toplevel_anonymous_class", False):
+                newContent.append(line.replace("System.out.println", "println").replace("System.out.print", "print"))
+            else:
+                newContent.append(line)
+
+    return "\n".join(newContent)
+
+def preprocess_section(context, section):
+    if "Chapter" in section:
+        section["Chapter"]["content"] = \
+            preprocess_content(context, section["Chapter"]["content"])
+        for sub_section in section["Chapter"].get("sub_items", []):
+            preprocess_section(context, sub_section)
+
+if __name__ == '__main__':
+    if len(sys.argv) > 1:
+        if sys.argv[1] == "supports":
+            sys.exit(0)
+
+    context, book = json.load(sys.stdin)
+
+    for section in book["sections"]:
+        preprocess_section(context, section)
+
+    print(json.dumps(book))

src/SUMMARY.md

@@ -20,6 +20,7 @@
 # Modern Java
 
 - [Prelude](./prelude.md)
+    - [Asking for Help](./prelude/asking_for_help.md)
     - [Toy Problems](./prelude/toy_problems.md)
 - [First Steps](./first_steps.md)
     - [Comments](./first_steps/comments.md)
@@ -88,6 +89,8 @@
     - [Multiline String Literals](./strings/multiline.md)
     - [Concatenation](./strings/concatenation.md)
     - [Equality](./strings/equality.md)
+    - [Length](./strings/length.md)
+    - [Access Individual Characters](./strings/access_individual_characters.md)
     - [Challenges](./strings/challenges.md)
 
 # Control Flow I
@@ -98,12 +101,14 @@
     - [Else If](./branching_logic/else_if.md)
     - [Relation to Delayed Assignment](./branching_logic/relation_to_delayed_assignment.md)
     - [Ternary Expression](./branching_logic/ternary_expression.md)
+    - [Challenges](./branching_logic/challenges.md)
 - [Loops](./loops.md)
     - [While](./loops/while.md)
     - [Termination Conditions](./loops/termination_conditions.md)
     - [Break](./loops/break.md)
     - [Continue](./loops/continue.md)
     - [Do](./loops/do.md)
+    - [Challenges](./loops/challenges.md)
 
 # User Defined Types
 

src/boolean/challenges.md

@@ -9,6 +9,23 @@ Remember the rules for this are
 
 What will this program output when run? Write down your guess and then try running it.
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    boolean a = true;
+    boolean b = false;
+    boolean c = true;
+    boolean d = false;
+
+    boolean result = a || b && c || !d;
+
+    System.out.println(result);
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -24,10 +41,29 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 ## Challenge 2
 
 What will this program output when run? Write down your guess and then try running it.
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    boolean a = true;
+    boolean b = false;
+    boolean c = true;
+    boolean d = false;
+
+    boolean result = !(a || b && c || !d) || (a && b || c);
+
+    System.out.println(result);
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -43,10 +79,28 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 ## Challenge 3
 
 Say you have two boolean variables, how could you use the operators we've covered to get the "exclusive or" of the two.
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    // Change these two variables to test your solution
+    boolean hasIceCream = true;
+    boolean hasCookie = false;
+
+    boolean validChoice = < YOUR CODE HERE >;
+
+    System.out.println(validChoice);
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -61,6 +115,8 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 Make sure to test all the possibilities.
 
 | hasIceCream | hasCookie | validChoice |

src/branching_logic/challenges.md

@@ -0,0 +1 @@
+# Challenges

src/characters/challenges.md

@@ -11,6 +11,18 @@ A lot of math problems ask you to find \\( x^2 \\). What is the value of the cha
 
 Try to work it out on paper before running the program below.
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    char x = 'x';
+
+    System.out.println(x * x);
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -21,12 +33,28 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 ## Challenge 2
 
 Alter the program below so that it will output `true` if the character declared at the top is a letter.
 
 Make use of the fact that the numeric values for `a` - `z` and `A` - `Z` are contiguous.
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    char c = 'a';
+
+    boolean isLetter = ???;
+
+    System.out.println(isLetter);
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -39,6 +67,8 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 ## Challenge 3
 
 How many UTF-16 code units does it take to represent this emoji? `👨‍🍳`.

src/first_steps.md

@@ -2,6 +2,16 @@
 
 If you made it through the [Getting Started section](./getting_started/hello_world.md) you've successfully run this program.
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    System.out.println("Hello, World!");
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -10,11 +20,26 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 This "prints" - not in the sense of a physical printer, but like "displays on the screen" -
 the text `"Hello, World!"`.
 
-Its a tradition for this to be your first program in
-any language. Unfortunately, for reasons that are impossible to explain with the context you have at this point,
+Its a tradition for this to be your first program in any language.
+~IF toplevel_anonymous_class
+
+We aren't quite at the point where I can explain what `void main()` means, but
+all you need to know for now is that it is what Java looks for to know where to start the program.
+
+```java
+void main() {
+    < WRITE YOUR CODE HERE >
+}
+```
+
+~ELSE
+
+Unfortunately, for reasons that are impossible to explain with the context you have at this point,
 half of this probably reads as cryptic nonsense.
 
 ```java
@@ -33,6 +58,8 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 So for all intents and purposes, this is the whole program.
 
 ```java
@@ -51,6 +78,20 @@ System.out.print("World");
 System.out.println("!");
 ```
 
+~IF toplevel_anonymous_class
+
+Which, when we add back `void main()`, looks like this.
+
+```java
+void main() {
+    System.out.print("Hello, ");
+    System.out.print("World");
+    System.out.println("!");
+}
+```
+
+~ELSE
+
 Which, when we add back the part you are squinting past, looks like this.
 
 ```java
@@ -63,6 +104,8 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 You should get in the habit of, whenever you see some bit of code, trying to physically type it out, run it,
 tweak it, and play with it.
 

src/first_steps/challenges.md

@@ -21,6 +21,23 @@ Jasmine
 
 What will this program output when run? Write down your guess and then try actually running it.
 
+~IF toplevel_anonymous_class
+
+```text
+void main() {
+    System.out.println("A");
+    //System.out.println("B");
+    System.out.println("C");//
+    System.out.println("D");
+    /*
+    System.out.println("E");
+    System.out.println("F");*/
+    System.out.println("G");
+}
+```
+
+~ELSE
+
 ```text
 public class Main {
     public static void main(String[] args) {
@@ -36,12 +53,27 @@ public class Main {
 }
 ```
 
+~ENDIF
+
 ## Challenge 3
 
 There are four semicolons in this perfectly functional program. Delete one of them at random and see what the errors you get look like.
 
 How could you use that error to figure out where you might have forgotten to put a semicolon?
 
+~IF toplevel_anonymous_class
+
+```java
+void main() {
+    System.out.println("Apple");
+    System.out.println("Banana");
+    System.out.println("Clementine");
+    System.out.println("Durian");
+}
+```
+
+~ELSE
+
 ```java
 public class Main {
     public static void main(String[] args) {
@@ -52,3 +84,5 @@ public class Main {
     }
 }
 ```
+
+~ENDIF