Restructures demos.

demos/java/.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11"/>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+	<classpathentry exported="true" kind="lib" path="lib/jackson-annotations-2.9.8.jar"/>
+	<classpathentry exported="true" kind="lib" path="lib/jackson-core-2.9.8.jar"/>
+	<classpathentry exported="true" kind="lib" path="lib/jackson-databind-2.9.8.jar"/>
+</classpath>

demos/java/.gitignore

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+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
+
+!lib/**

demos/java/.project

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<projectDescription>
+  <name>java</name>
+  <comment/>
+  <projects>&#xD;
+    </projects>
+  <buildSpec>
+    <buildCommand>
+      <name>org.eclipse.jdt.core.javabuilder</name>
+      <arguments>&#xD;
+            </arguments>
+    </buildCommand>
+  </buildSpec>
+  <natures>
+    <nature>org.eclipse.jdt.core.javanature</nature>
+  </natures>
+</projectDescription>

demos/java/.settings/org.eclipse.jdt.core.prefs

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+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=11
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=10
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.source=11

demos/java/.vscode/launch.json

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+{
+	// Use IntelliSense to find out which attributes exist for C# debugging
+	// Use hover for the description of the existing attributes
+	// For further information visit https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md
+	"version": "0.2.0",
+	"configurations": [
+		{
+			"type": "java",
+			"name": "CodeLens (Launch) - DemoLinkedLists",
+			"request": "launch",
+			"mainClass": "DemoLinkedLists"
+		},
+		{
+			"name": "Java - Demo",
+			"type": "java",
+			"request": "launch",
+			"projectName": "java"
+		}
+	]
+}

demos/java/.vscode/settings.json

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+{
+	"java.dependency.packagePresentation": "flat",
+	"java.dependency.syncWithFolderExplorer": true,
+	"debugVisualizer.debugAdapterConfigurations": {}
+}

demos/java/src/app/App.java

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+package app;
+
+import app.GraphData.EdgeInfo;
+
+public class App {
+
+    public static void main(String[] args) {
+        // watch `list.visualize()`
+        LinkedList<String> list = new LinkedList<String>();
+        list.append("1");
+        list.append("2");
+        list.append("3");
+        list.append("4");
+    }
+}
+
+class LinkedList<T> {
+    private Node<T> head;
+
+    public void append(T value) {
+        if (head == null) {
+            head = new Node<T>(value);
+        } else {
+            Node<T> m = head;
+            while (m.next != null) {
+                m = m.next;
+            }
+            m.next = new Node<T>(value);
+        }
+    }
+
+    public String visualize() {
+        Node<T> list = new Node<T>(null);
+        list.next = this.head;
+
+        return GraphData.from(list, (item, info) -> {
+            if (item != list) {
+                info.id = item.value.toString();
+            } else {
+                info.label = "list";
+            }
+            if (item.next != null) {
+                EdgeInfo<LinkedList.Node<T>> ei = info.addEdge(item.next);
+                ei.label = "next";
+            }
+            return info;
+        }).toString();
+    }
+
+    static class Node<T> {
+        public T value;
+        public Node<T> next;
+
+        public Node(T value) {
+            this.value = value;
+        }
+    }
+}

demos/java/src/app/ExtractedData.java

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+package app;
+
+import java.util.HashMap;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public abstract class ExtractedData {
+    public HashMap<String, Boolean> getKind() {
+        HashMap<String, Boolean> m = new HashMap<>();
+        for (String s : getTags()) {
+            m.put(s, true);
+        }
+        return m;
+    }
+
+    @JsonIgnore
+    protected abstract String[] getTags();
+
+    @Override
+    public String toString() {
+        ObjectMapper objectMapper = new ObjectMapper();
+        try {
+            String val = objectMapper.writeValueAsString(this);
+            return val;
+        } catch (JsonProcessingException e) {
+            return "JsonProcessingException";
+        }
+    }
+}

demos/java/src/app/GraphData.java

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+package app;
+
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
+
+public class GraphData extends ExtractedData {
+    private List<NodeData> nodes = new ArrayList<>();
+    private List<EdgeData> edges = new ArrayList<>();
+
+    @Override
+    protected String[] getTags() {
+        return new String[] { "graph" };
+    }
+
+    public List<NodeData> getNodes() {
+        return this.nodes;
+    }
+
+    public List<EdgeData> getEdges() {
+        return this.edges;
+    }
+
+    @JsonInclude(Include.NON_NULL)
+    public static class NodeData {
+        private String id;
+        private String label; // can be null
+        private String color; // can be null
+        private String shape; // can be null
+
+        public NodeData(String id) {
+            this.id = id;
+        }
+
+        public String getId() {
+            return this.id;
+        }
+
+        public void setId(String id) {
+            this.id = id;
+        }
+
+        public String getLabel() {
+            return this.label;
+        }
+
+        public void setLabel(String label) {
+            this.label = label;
+        }
+
+        public String getColor() {
+            return this.color;
+        }
+
+        public void setColor(String color) {
+            this.color = color;
+        }
+
+        public String getShape() {
+            return this.shape;
+        }
+
+        public void setShape(String shape) {
+            this.shape = shape;
+        }
+    }
+
+    @JsonInclude(Include.NON_NULL)
+    public static class EdgeData {
+        private String from;
+        private String to;
+        private String label; // Can be null
+        private String id; // Can be null
+        private String color; // Can be null
+        private Boolean dashes; // Can be null
+
+        public EdgeData(String from, String to) {
+            this.from = from;
+            this.to = to;
+        }
+
+        public String getFrom() {
+            return this.from;
+        }
+
+        public void setFrom(String from) {
+            this.from = from;
+        }
+
+        public String getTo() {
+            return this.to;
+        }
+
+        public void setTo(String to) {
+            this.to = to;
+        }
+
+        public String getLabel() {
+            return this.label;
+        }
+
+        public void setLabel(String label) {
+            this.label = label;
+        }
+
+        public String getId() {
+            return this.id;
+        }
+
+        public void setId(String id) {
+            this.id = id;
+        }
+
+        public String getColor() {
+            return this.color;
+        }
+
+        public void setColor(String color) {
+            this.color = color;
+        }
+
+        public Boolean getDashes() {
+            return this.dashes;
+        }
+
+        public void setDashes(Boolean dashes) {
+            this.dashes = dashes;
+        }
+    }
+
+    public interface NodeInfoProvider<T> {
+        public NodeInfo<T> getNodeInfo(T item, NodeInfo<T> nodeInfo);
+    }
+
+    public static <T> GraphData from(T item, NodeInfoProvider<T> f) {
+        GraphData d = new GraphData();
+        ArrayDeque<T> q = new ArrayDeque<>();
+        q.add(item);
+
+        FromState<T> s = new FromState<>(f);
+
+        while (q.size() > 0) {
+            NodeInfo<T> nodeInfo = s.getNodeInfo(q.removeFirst());
+            NodeData nd = new NodeData(s.getId(nodeInfo));
+            d.nodes.add(nd);
+
+            nd.setLabel(nodeInfo.label);
+            nd.setColor(nodeInfo.color);
+
+            for (EdgeInfo<T> e : nodeInfo.edges) {
+                EdgeData ed = new EdgeData(nd.id, s.getId(s.getNodeInfo(e.to)));
+                d.edges.add(ed);
+                ed.setLabel(e.label);
+                ed.setId(e.id);
+
+                q.add(e.to);
+            }
+
+        }
+
+        return d;
+    }
+
+    static class FromState<T> {
+        private int i = 0;
+        private NodeInfoProvider<T> provider;
+        private HashMap<T, NodeInfo<T>> infos = new HashMap<>();
+
+        public FromState(NodeInfoProvider<T> provider) {
+            this.provider = provider;
+        }
+
+        public String getId(NodeInfo<T> nodeInfo) {
+            if (nodeInfo.id == null) {
+                nodeInfo.id = "hediet.de/" + (i++);
+            }
+            return nodeInfo.id;
+        }
+
+        public NodeInfo<T> getNodeInfo(T item) {
+            if (infos.containsKey(item)) {
+                return infos.get(item);
+            }
+
+            NodeInfo<T> info = this.provider.getNodeInfo(item, new NodeInfo<>());
+            infos.put(item, info);
+            return info;
+        }
+    }
+
+    public static class NodeInfo<T> {
+        public ArrayList<EdgeInfo<T>> edges = new ArrayList<EdgeInfo<T>>();
+        public String label; // Can be null.
+        public String id; // Can be null.
+        public String color; // Can be null.
+
+        public EdgeInfo<T> addEdge(T to) {
+            EdgeInfo<T> i = new EdgeInfo<>(to);
+            this.edges.add(i);
+            return i;
+        }
+    }
+
+    public static class EdgeInfo<T> {
+        public T to;
+        public String label; // Can be null.
+        public String id; // Can be null.
+
+        public EdgeInfo(T to) {
+            this.to = to;
+        }
+    }
+}

demos/java/src/app/TextData.java

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+package app;
+
+public class TextData extends ExtractedData {
+    private final String textValue;
+
+    public TextData(String text) {
+        this.textValue = text;
+    }
+
+    @Override
+    protected String[] getTags() {
+        return new String[] { "text" };
+    }
+
+    public String getText() {
+        return this.textValue;
+    }
+}