sealed: add release-level and Jackson 3.2.3 transcripts
09 shows which language level each sealed feature needs; 10 runs the Payment model through Jackson 3 (jars fetched and sha1-checked, not committed). Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a
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Claude
@@ -10,6 +10,7 @@ JDK25=/path/to/jdk-25 JDK27=/path/to/jdk-27 [JDK21=/path/to/jdk-21] ./run.sh
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- `src/` compiles and runs unchanged on 21, 25 and 27: the `Payment` model, the three subclass modifiers, generic and recursive hierarchies, the `default` trap and a visitor for comparison.
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- `broken/` fails to compile on purpose (one rule per file).
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- `sep/` shows what the JVM itself enforces when a class file disagrees with the sealed type it claims to extend.
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- `jackson/` runs the same `Payment` through Jackson 3.2.3 (`./jackson/fetch.sh` downloads and sha1-checks the three jars from Maven Central; they are not committed).
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- `multi/` is a named module, the only place a sealed hierarchy may span packages.
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Tested on Temurin 25.0.4.1+1 and 27+35, and OpenJDK 21.0.10 as the baseline.
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@@ -0,0 +1 @@
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lib/
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@@ -0,0 +1,25 @@
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import com.fasterxml.jackson.annotation.JsonSubTypes;
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import com.fasterxml.jackson.annotation.JsonTypeInfo;
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import tools.jackson.databind.json.JsonMapper;
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public class JsonForgotten {
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// Wallet is a permitted subtype, and the compiler is happy, but nobody told Jackson about it.
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@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
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@JsonSubTypes({
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@JsonSubTypes.Type(value = Card.class, name = "card"),
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@JsonSubTypes.Type(value = Upi.class, name = "upi")})
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sealed interface Payment permits Card, Upi, Wallet {}
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record Card(long amount) implements Payment {}
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record Upi(long amount) implements Payment {}
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record Wallet(long amount) implements Payment {}
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public static void main(String[] args) {
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JsonMapper mapper = JsonMapper.builder().build();
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System.out.println("write : " + mapper.writeValueAsString(new Wallet(500)));
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try {
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mapper.readValue("{\"type\":\"wallet\",\"amount\":500}", Payment.class);
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} catch (Exception e) {
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System.out.println("read : " + e.getClass().getSimpleName() + ": " + e.getMessage().lines().findFirst().orElse(""));
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}
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}
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}
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@@ -0,0 +1,32 @@
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import com.fasterxml.jackson.annotation.JsonTypeInfo;
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import tools.jackson.databind.json.JsonMapper;
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public class JsonNoSubTypes {
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// Only @JsonTypeInfo, no @JsonSubTypes. Does Jackson find the permitted subclasses by itself?
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@JsonTypeInfo(use = JsonTypeInfo.Id.SIMPLE_NAME, property = "type")
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sealed interface Payment permits Card, Upi {}
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record Card(long amount) implements Payment {}
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record Upi(long amount) implements Payment {}
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// Control: the same shape without the word sealed.
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@JsonTypeInfo(use = JsonTypeInfo.Id.SIMPLE_NAME, property = "type")
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interface OpenPayment {}
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record OpenCard(long amount) implements OpenPayment {}
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static void tryRead(JsonMapper m, String label, String json, Class<?> type) {
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try {
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System.out.println(label + ": " + m.readValue(json, type));
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} catch (Exception e) {
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System.out.println(label + ": " + e.getClass().getSimpleName() + ": " + e.getMessage().lines().findFirst().orElse(""));
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}
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}
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public static void main(String[] args) {
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JsonMapper m = JsonMapper.builder().build();
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System.out.println("write : " + m.writeValueAsString(new Card(500)));
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tryRead(m, "sealed, Card ", "{\"type\":\"Card\",\"amount\":500}", Payment.class);
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tryRead(m, "sealed, Upi ", "{\"type\":\"Upi\",\"amount\":500}", Payment.class);
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tryRead(m, "sealed, Cheque", "{\"type\":\"Cheque\",\"amount\":500}", Payment.class);
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tryRead(m, "plain, OpenCard", "{\"type\":\"OpenCard\",\"amount\":500}", OpenPayment.class);
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}
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}
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@@ -0,0 +1,39 @@
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import com.fasterxml.jackson.annotation.JsonSubTypes;
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import com.fasterxml.jackson.annotation.JsonTypeInfo;
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import tools.jackson.databind.json.JsonMapper;
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public class JsonPayment {
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// Two annotations tell Jackson which JSON field names the type, and which class each name means.
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@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
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@JsonSubTypes({
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@JsonSubTypes.Type(value = Card.class, name = "card"),
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@JsonSubTypes.Type(value = Upi.class, name = "upi"),
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@JsonSubTypes.Type(value = NetBanking.class, name = "netbanking")})
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sealed interface Payment permits Card, Upi, NetBanking {}
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record Card(String last4, long amount) implements Payment {}
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record Upi(String vpa, long amount) implements Payment {}
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record NetBanking(String bank, long amount) implements Payment {}
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static long fee(Payment p) {
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return switch (p) {
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case Card(String last4, long amount) -> amount * 2 / 100;
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case Upi(String vpa, long amount) -> 0;
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case NetBanking(String bank, long amount) -> 15;
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};
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}
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public static void main(String[] args) {
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JsonMapper mapper = JsonMapper.builder().build();
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Payment[] all = { new Card("4242", 500), new Upi("ankur@bank", 500), new NetBanking("HDFC", 500) };
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for (Payment p : all) {
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String json = mapper.writeValueAsString(p);
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Payment back = mapper.readValue(json, Payment.class);
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System.out.println(json + " -> " + back + " equal=" + back.equals(p) + " fee=" + fee(back));
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}
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try {
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mapper.readValue("{\"type\":\"cheque\",\"amount\":500}", Payment.class);
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} catch (Exception e) {
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System.out.println("unknown type: " + e.getClass().getSimpleName() + ": " + e.getMessage().lines().findFirst().orElse(""));
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}
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}
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}
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Executable
+13
@@ -0,0 +1,13 @@
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#!/usr/bin/env bash
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# Downloads the three Jackson jars from Maven Central into ./lib and checks each against the published .sha1
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set -euo pipefail
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cd "$(dirname "$0")"; mkdir -p lib
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M=https://repo1.maven.org/maven2
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for a in tools/jackson/core/jackson-databind/3.2.3/jackson-databind-3.2.3 \
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tools/jackson/core/jackson-core/3.2.3/jackson-core-3.2.3 \
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com/fasterxml/jackson/core/jackson-annotations/2.22/jackson-annotations-2.22; do
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f="lib/$(basename "$a").jar"
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[ -f "$f" ] || curl -sfL -o "$f" "$M/$a.jar"
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want="$(curl -sfL "$M/$a.jar.sha1" | cut -d' ' -f1)"; got="$(sha1sum "$f" | cut -d' ' -f1)"
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[ "$want" = "$got" ] && echo "ok $f $got" || { echo "SHA1 MISMATCH $f"; exit 1; }
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done
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@@ -0,0 +1,17 @@
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$ javac --release 16 src/ImplicitPermits.java (25.0.4.1+1-LTS)
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src/ImplicitPermits.java:4: error: sealed classes are not supported in -source 16
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public sealed class ImplicitPermits {
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^
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(use -source 17 or higher to enable sealed classes)
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1 error
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exit=1
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$ javac --release 17 src/ImplicitPermits.java (25.0.4.1+1-LTS)
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exit=0
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$ javac --release 17 src/PaymentDemo.java (25.0.4.1+1-LTS)
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src/PaymentDemo.java:11: error: patterns in switch statements are not supported in -source 17
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case Card(String last4, long amount) -> amount * 2 / 100; // 2 percent
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^
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(use -source 21 or higher to enable patterns in switch statements)
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src/PaymentDemo.java:11: error: deconstruction patterns are not supported in -source 17
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@@ -0,0 +1,50 @@
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$ javac -cp jackson/lib/* jackson/JsonPayment.java && java JsonPayment (21.0.10+7-Ubuntu-124.04)
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{"type":"card","last4":"4242","amount":500} -> Card[last4=4242, amount=500] equal=true fee=10
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{"type":"upi","vpa":"ankur@bank","amount":500} -> Upi[vpa=ankur@bank, amount=500] equal=true fee=0
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{"type":"netbanking","bank":"HDFC","amount":500} -> NetBanking[bank=HDFC, amount=500] equal=true fee=15
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unknown type: InvalidTypeIdException: Could not resolve type id 'cheque' as a subtype of `JsonPayment$Payment`: known type ids = [card, netbanking, upi]
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$ javac -cp jackson/lib/* jackson/JsonPayment.java && java JsonPayment (25.0.4.1+1-LTS)
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{"type":"card","last4":"4242","amount":500} -> Card[last4=4242, amount=500] equal=true fee=10
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{"type":"upi","vpa":"ankur@bank","amount":500} -> Upi[vpa=ankur@bank, amount=500] equal=true fee=0
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{"type":"netbanking","bank":"HDFC","amount":500} -> NetBanking[bank=HDFC, amount=500] equal=true fee=15
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unknown type: InvalidTypeIdException: Could not resolve type id 'cheque' as a subtype of `JsonPayment$Payment`: known type ids = [card, netbanking, upi]
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$ javac -cp jackson/lib/* jackson/JsonPayment.java && java JsonPayment (27+35)
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{"type":"card","last4":"4242","amount":500} -> Card[last4=4242, amount=500] equal=true fee=10
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{"type":"upi","vpa":"ankur@bank","amount":500} -> Upi[vpa=ankur@bank, amount=500] equal=true fee=0
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{"type":"netbanking","bank":"HDFC","amount":500} -> NetBanking[bank=HDFC, amount=500] equal=true fee=15
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unknown type: InvalidTypeIdException: Could not resolve type id 'cheque' as a subtype of `JsonPayment$Payment`: known type ids = [card, netbanking, upi]
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$ javac -cp jackson/lib/* jackson/JsonForgotten.java && java JsonForgotten (21.0.10+7-Ubuntu-124.04)
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write : {"type":"JsonForgotten$Wallet","amount":500}
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read : InvalidTypeIdException: Could not resolve type id 'wallet' as a subtype of `JsonForgotten$Payment`: known type ids = [card, upi]
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$ javac -cp jackson/lib/* jackson/JsonForgotten.java && java JsonForgotten (25.0.4.1+1-LTS)
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write : {"type":"JsonForgotten$Wallet","amount":500}
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read : InvalidTypeIdException: Could not resolve type id 'wallet' as a subtype of `JsonForgotten$Payment`: known type ids = [card, upi]
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$ javac -cp jackson/lib/* jackson/JsonForgotten.java && java JsonForgotten (27+35)
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write : {"type":"JsonForgotten$Wallet","amount":500}
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read : InvalidTypeIdException: Could not resolve type id 'wallet' as a subtype of `JsonForgotten$Payment`: known type ids = [card, upi]
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$ javac -cp jackson/lib/* jackson/JsonNoSubTypes.java && java JsonNoSubTypes (21.0.10+7-Ubuntu-124.04)
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write : {"type":"Card","amount":500}
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sealed, Card : Card[amount=500]
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sealed, Upi : Upi[amount=500]
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sealed, Cheque: InvalidTypeIdException: Could not resolve type id 'Cheque' as a subtype of `JsonNoSubTypes$Payment`: known type ids = [Card, Upi]
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plain, OpenCard: InvalidTypeIdException: Could not resolve type id 'OpenCard' as a subtype of `JsonNoSubTypes$OpenPayment`: known type ids = []
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$ javac -cp jackson/lib/* jackson/JsonNoSubTypes.java && java JsonNoSubTypes (25.0.4.1+1-LTS)
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write : {"type":"Card","amount":500}
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sealed, Card : Card[amount=500]
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sealed, Upi : Upi[amount=500]
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sealed, Cheque: InvalidTypeIdException: Could not resolve type id 'Cheque' as a subtype of `JsonNoSubTypes$Payment`: known type ids = [Card, Upi]
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plain, OpenCard: InvalidTypeIdException: Could not resolve type id 'OpenCard' as a subtype of `JsonNoSubTypes$OpenPayment`: known type ids = []
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$ javac -cp jackson/lib/* jackson/JsonNoSubTypes.java && java JsonNoSubTypes (27+35)
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write : {"type":"Card","amount":500}
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sealed, Card : Card[amount=500]
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sealed, Upi : Upi[amount=500]
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sealed, Cheque: InvalidTypeIdException: Could not resolve type id 'Cheque' as a subtype of `JsonNoSubTypes$Payment`: known type ids = [Card, Upi]
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plain, OpenCard: InvalidTypeIdException: Could not resolve type id 'OpenCard' as a subtype of `JsonNoSubTypes$OpenPayment`: known type ids = []
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@@ -56,4 +56,19 @@ mm() { local jdk="$1" o; o="$(mk)"
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echo "\$ javac -d out \$(find multi/demo.pay -name '*.java') && java -p out -m demo.pay/pay.app.Main ($(t "$jdk"))"
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"$jdk/bin/javac" -d "$o" $(find multi/demo.pay -name '*.java') 2>&1 && "$jdk/bin/java" -p "$o" -m demo.pay/pay.app.Main 2>&1; }
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{ all3 mm; } > "$OUT/08-modules.txt"
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# 09 - which language level each feature needs (sealed is final in 17; a switch over the sealed type needs 21)
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rl() { local jdk="$1" rel="$2" src="$3" o; o="$(mk)"
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echo "\$ javac --release $rel $src ($(t "$jdk"))"
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"$jdk/bin/javac" --release "$rel" -d "$o" "$src" 2>&1 | grep -v '^Note:'; echo "exit=${PIPESTATUS[0]}"; }
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{ rl "$JDK25" 16 src/ImplicitPermits.java; echo; rl "$JDK25" 17 src/ImplicitPermits.java; echo; rl "$JDK25" 17 src/PaymentDemo.java | head -6; } > "$OUT/09-release-levels.txt"
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# 10 - Jackson 3.2.3: does a sealed type help JSON polymorphism? (needs jackson/fetch.sh first; jars are not committed)
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jj() { local jdk="$1" src="$2" cls="$3" o cp; o="$(mk)"
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cp="jackson/lib/jackson-databind-3.2.3.jar:jackson/lib/jackson-core-3.2.3.jar:jackson/lib/jackson-annotations-2.22.jar"
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echo "\$ javac -cp jackson/lib/* $src && java $cls ($(t "$jdk"))"
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"$jdk/bin/javac" -cp "$cp" -d "$o" "$src" 2>&1 && "$jdk/bin/java" -cp "$cp:$o" "$cls" 2>&1; }
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if [ -f jackson/lib/jackson-databind-3.2.3.jar ]; then
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{ all3 jj jackson/JsonPayment.java JsonPayment; echo; all3 jj jackson/JsonForgotten.java JsonForgotten; echo; all3 jj jackson/JsonNoSubTypes.java JsonNoSubTypes; } > "$OUT/10-jackson.txt"
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else echo "skipped 10-jackson.txt: run jackson/fetch.sh first"; fi
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echo done
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