Claude
e0cb6e83e2
Runnable sources, broken examples and captured transcripts for the ankurm.com JEP 512 article, including the measured launch order and a private-constructor difference between 25 and 27. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a
114 lines
6.0 KiB
Bash
Executable File
114 lines
6.0 KiB
Bash
Executable File
#!/usr/bin/env bash
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# JEP 512 (Compact Source Files and Instance Main Methods): final in JDK 25, no --enable-preview.
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# Regenerates every file in output/. Needs JDK 25 and JDK 27; a JDK 21 is optional (for the "before" transcript).
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# JDK25=/path JDK27=/path [JDK21=/path] ./run.sh
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set -uo pipefail
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unset JAVA_TOOL_OPTIONS
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HERE="$(cd "$(dirname "$0")" && pwd)"
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JDK25="${JDK25:-/opt/jdks/jdk-25.0.4.1+1}"; JDK27="${JDK27:-/opt/jdks/jdk27}"; JDK21="${JDK21:-}"
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OUT="$HERE/output"; mkdir -p "$OUT"; B="$(mktemp -d)"; trap 'rm -rf "$B"' EXIT
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cd "$HERE"
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v() { "$1/bin/java" -version 2>&1 | sed -n 2p; } # runtime line only, no vendor banner noise
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# 01 - the source launcher: one command, no javac, no class file left behind
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{
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echo "\$ cat src/Hello.java"; cat src/Hello.java; echo
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echo "\$ java src/Hello.java (JDK 25: $(v $JDK25))"; "$JDK25/bin/java" src/Hello.java 2>&1
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echo; echo "\$ java src/Hello.java (JDK 27: $(v $JDK27))"; "$JDK27/bin/java" src/Hello.java 2>&1
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echo; echo "\$ ls src/*.class"; ls src/*.class 2>&1 | sed 's/^/ /'
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if [ -n "$JDK21" ]; then
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echo; echo "\$ java src/Hello.java (JDK 21: $(v $JDK21))"; "$JDK21/bin/java" src/Hello.java 2>&1
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fi
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} > "$OUT/01-source-launcher.txt"
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# 02 - javac produces an ordinary class file; javap shows what the compiler invented
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{
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echo "\$ javac -d out src/Hello.java && java -cp out Hello"
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"$JDK25/bin/javac" -d "$B/o" src/Hello.java 2>&1 && "$JDK25/bin/java" -cp "$B/o" Hello 2>&1
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echo; echo "\$ javap -p -cp out Hello"; "$JDK25/bin/javap" -p -cp "$B/o" Hello 2>&1
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echo; echo "\$ javap -v -cp out Hello | grep -E 'major|flags'"
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"$JDK25/bin/javap" -v -cp "$B/o" Hello 2>&1 | grep -E 'major version|^ flags' | head -2
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echo; echo "\$ java Reflect (asks the loaded class)"
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"$JDK25/bin/javac" -cp "$B/o" -d "$B/o" src/Reflect.java 2>&1 && "$JDK25/bin/java" -cp "$B/o" Reflect 2>&1
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} > "$OUT/02-javac-and-javap.txt"
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# 03 - the class body: members, nested types, implicit imports
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{
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echo "\$ java src/Members.java"; "$JDK25/bin/java" src/Members.java 2>&1
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echo; echo "\$ java src/WithArgs.java one two"; "$JDK25/bin/java" src/WithArgs.java one two 2>&1
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echo; echo "\$ java src/InstanceMainInClass.java"; "$JDK25/bin/java" src/InstanceMainInClass.java 2>&1
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echo; echo "\$ java src/NeedsImport.java (java.net.http is outside java.base: a normal import fixes it)"; "$JDK25/bin/java" src/NeedsImport.java 2>&1
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echo; echo "\$ java src/NeedsModuleImport.java (or import the whole module)"; "$JDK25/bin/java" src/NeedsModuleImport.java 2>&1
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echo; echo "\$ java multi/App.java (App.java + Greeter.java in one directory)"; "$JDK25/bin/java" multi/App.java 2>&1
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} > "$OUT/03-members-and-imports.txt"
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# 04 - the IO helper
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{
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echo "\$ printf 'Ankur\n30\n' | java src/ReadLn.java"; printf 'Ankur\n30\n' | "$JDK25/bin/java" src/ReadLn.java 2>&1
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echo; echo "\$ java src/IoInAnyClass.java"; "$JDK25/bin/java" src/IoInAnyClass.java 2>&1
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echo; echo "\$ java src/StaticImportIO.java (import static java.lang.IO.* makes the bare form work)"; "$JDK25/bin/java" src/StaticImportIO.java 2>&1
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echo; echo "\$ java broken/NoIoPrefix.java (JDK 27: same error as on 25)"; "$JDK27/bin/java" broken/NoIoPrefix.java 2>&1 | head -8
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echo; echo "\$ printf '' | java src/ReadLn.java (stdin closed: what does readln return?)"
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printf '' | "$JDK25/bin/java" src/ReadLn.java 2>&1
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} > "$OUT/04-io-helper.txt"
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# 05 - which main wins. Generate every pair of mains that can coexist and ask the launcher.
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gen() { # name, body
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printf 'class %s {\n%s\n}\n' "$1" "$2" > "$B/$1.java"
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}
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gen SS_i0 ' static void main(String[] a) { IO.println("static main(String[])"); }
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void main() { IO.println("instance main()"); }'
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gen S0_iS ' static void main() { IO.println("static main()"); }
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void main(String[] a) { IO.println("instance main(String[])"); }'
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gen SS_S0 ' static void main(String[] a) { IO.println("static main(String[])"); }
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static void main() { IO.println("static main()"); }'
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gen IS_I0 ' void main(String[] a) { IO.println("instance main(String[])"); }
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void main() { IO.println("instance main()"); }'
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{
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for j in "$JDK25" "$JDK27"; do
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echo "== $(v $j)"
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for c in SS_i0 S0_iS SS_S0 IS_I0; do
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printf '%-8s declares: %-58s -> ran: ' "$c" "$(grep -o '\(static \)\?void main([^)]*)' "$B/$c.java" | tr '\n' ' ')"
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"$j/bin/java" "$B/$c.java" 2>&1 | head -1
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done
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echo "-- same four classes, compiled first and launched as a class (java -cp out NAME)"
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rm -rf "$B/cls"; mkdir -p "$B/cls"; "$j/bin/javac" -d "$B/cls" "$B"/SS_i0.java "$B"/S0_iS.java "$B"/SS_S0.java "$B"/IS_I0.java 2>&1
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for c in SS_i0 S0_iS SS_S0 IS_I0; do
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printf '%-8s -> ran: ' "$c"; "$j/bin/java" -cp "$B/cls" "$c" 2>&1 | head -1
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done
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echo
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done
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} > "$OUT/05-launch-order.txt"
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# 06 - every way to get it wrong, with the compiler's own words
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{
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for f in NoMain NoIoPrefix NotInJavaBase WithPackage Other WrongParam PrivateMain CtorWithArgs; do
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if [ "$f" = Other ]; then
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echo "\$ javac -d out broken/Other.java broken/Target.java (JDK 25; Target.java is a compact file)"
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"$JDK25/bin/javac" -d "$B/x" broken/Other.java broken/Target.java 2>&1 | head -12
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echo; echo "\$ java broken/Other.java (JDK 25; source launcher, Target.java sits next to it)"
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"$JDK25/bin/java" broken/Other.java 2>&1 | head -12
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else
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echo "\$ java broken/$f.java (JDK 25)"; "$JDK25/bin/java" broken/$f.java 2>&1 | head -12
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fi
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echo
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done
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} > "$OUT/06-compile-errors.txt"
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# 07 - the one behaviour that differs between 25 and 27
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{
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for j in "$JDK25" "$JDK27"; do
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echo "\$ java broken/PrivateCtor.java ($(v $j))"
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"$j/bin/java" broken/PrivateCtor.java 2>&1 | head -6; echo
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done
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} > "$OUT/07-private-constructor-25-vs-27.txt"
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# 08 - what java.lang.IO actually is
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{
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echo "\$ javap -p java.lang.IO"; "$JDK25/bin/javap" -p java.lang.IO 2>&1
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echo; echo "\$ javap -p -c java.lang.IO | grep -E 'public static|System.out|readLine|IOError'"
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"$JDK25/bin/javap" -p -c java.lang.IO 2>&1 | grep -E 'public static|System.out|readLine|IOError|flush'
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} > "$OUT/08-io-class.txt"
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echo "wrote $OUT"
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