diff --git a/pom.xml b/pom.xml
index a8e10323..8be3eff0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -109,6 +109,7 @@
                     <showWarnings>true</showWarnings>
                     <compilerArgs>
                          <arg>--enable-preview</arg>
+                         <arg>-Xlint:deprecation</arg>
                     </compilerArgs>
                 </configuration>
             </plugin>
diff --git a/src/main/java/de/learnlib/ralib/oracles/mto/LabeledSDT.java b/src/main/java/de/learnlib/ralib/oracles/mto/LabeledSDT.java
index 00006006..1b033835 100644
--- a/src/main/java/de/learnlib/ralib/oracles/mto/LabeledSDT.java
+++ b/src/main/java/de/learnlib/ralib/oracles/mto/LabeledSDT.java
@@ -1,10 +1,8 @@
 package de.learnlib.ralib.oracles.mto;
 
-import java.util.Arrays;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.Set;
 
 import de.learnlib.ralib.theory.SDT;
@@ -142,50 +140,4 @@ public static LabeledSDT pruneBranch(LabeledSDT lsdt, int label) {
 		return new LabeledSDT(lsdt, label);
 	}
 
-    @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        String regs = Arrays.toString(sdt.getRegisters().toArray());
-        sb.append(regs).append("-+\n");
-        toString(sb, spaces(regs.length()));
-        return sb.toString();
-    }
-
-    void toString(StringBuilder sb, String indentation) {
-    	if (sdt instanceof SDTLeaf) {
-    		sb.append(indentation).append("[Leaf").append(sdt.isAccepting() ? "+" : "-").append("]").append("\n");
-    	} else {
-	        LabeledSDT idioticSdt = this;
-	        sb.append(indentation).append("[]");
-	        final int childCount = idioticSdt.children.size();
-	        int count = 1;
-	        for (Entry<SDTGuard, LabeledSDT> e : idioticSdt.children.entrySet()) {
-	            SDTGuard g = e.getKey();
-	            String gString = g.toString();
-	            String nextIndent;
-	            if (count == childCount) {
-	                nextIndent = indentation + "      ";
-	            } else {
-	                nextIndent = indentation + " |    ";
-	            }
-
-	            if (count > 1) {
-	                sb.append(indentation).append(" +");
-	            }
-	            sb.append("- ").append(e.getValue().label).append(":").append(gString).append("\n");
-	            e.getValue().toString(sb, nextIndent);
-
-	            count++;
-	        }
-    	}
-    }
-
-    private String spaces(int max) {
-        StringBuilder sb = new StringBuilder();
-        for (int i = 0; i < max; i++) {
-            sb.append(" ");
-        }
-        return sb.toString();
-    }
-
 }
diff --git a/src/main/java/de/learnlib/ralib/theory/SDT.java b/src/main/java/de/learnlib/ralib/theory/SDT.java
index 371e75e0..f05ac7f8 100644
--- a/src/main/java/de/learnlib/ralib/theory/SDT.java
+++ b/src/main/java/de/learnlib/ralib/theory/SDT.java
@@ -51,11 +51,11 @@ public SDT(Map<SDTGuard, SDT> children) {
      * @return
      */
     // todo: SDTs cannot have registers anymore, this should be data values!
-    // this method is currently only used in the toString methods of SDTs. Changing
-    // it will require changing many test cases as the toString methods are used
-    // to check the correctness of many SDTs.
+    // This private method is currently only used in the toString method of this
+    // class. Removing it will require changing many test cases as the toString
+    // method is used to check the correctness of many SDTs.
     @Deprecated
-    public Set<Register> getRegisters() {
+    private Set<Register> getRegisters() {
         Set<DataValue> temp = new LinkedHashSet<>();
         this.getVariables().stream().filter(SDTGuardElement::isDataValue).forEach((x) -> {
             temp.add((DataValue) x);
diff --git a/src/main/java/de/learnlib/ralib/theory/SDTLeaf.java b/src/main/java/de/learnlib/ralib/theory/SDTLeaf.java
index d237f03d..b29156fc 100644
--- a/src/main/java/de/learnlib/ralib/theory/SDTLeaf.java
+++ b/src/main/java/de/learnlib/ralib/theory/SDTLeaf.java
@@ -25,7 +25,6 @@
 
 import de.learnlib.ralib.data.SDTGuardElement;
 import de.learnlib.ralib.data.SDTRelabeling;
-import de.learnlib.ralib.data.SymbolicDataValue;
 
 /**
  * Leaf implementation of an SDT.
@@ -103,11 +102,6 @@ public Map<List<SDTGuard>, Boolean> getAllPaths(List<SDTGuard> path) {
     	return ret;
     }
 
-    @Override
-    public Set<SymbolicDataValue.Register> getRegisters() {
-        return new LinkedHashSet<>();
-    }
-
     @Override
     public Set<SDTGuardElement> getVariables() {
         return new LinkedHashSet<>();