diff --git a/sootup.callgraph/src/main/java/sootup/callgraph/AbstractCallGraphAlgorithm.java b/sootup.callgraph/src/main/java/sootup/callgraph/AbstractCallGraphAlgorithm.java
index be599ea6adc..95ff7c7588b 100644
--- a/sootup.callgraph/src/main/java/sootup/callgraph/AbstractCallGraphAlgorithm.java
+++ b/sootup.callgraph/src/main/java/sootup/callgraph/AbstractCallGraphAlgorithm.java
@@ -446,30 +446,16 @@ public CallGraph addClass(@Nonnull CallGraph oldCallGraph, @Nonnull JavaClassTyp
    * @return - MethodSignature of main method.
    */
   public MethodSignature findMainMethod() {
-    Set<SootClass> classes = new HashSet<>(); /* Set to track the classes to check */
-    for (SootClass aClass : view.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
-
-    Collection<SootMethod> mainMethods = new HashSet<>(); /* Set to store the methods */
-    for (SootClass aClass : classes) {
-      for (SootMethod method : aClass.getMethods()) {
-        if (method.isStatic()
-            && method
-                .getSignature()
-                .equals(
-                    JavaIdentifierFactory.getInstance()
-                        .getMethodSignature(
-                            aClass.getType(),
-                            "main",
-                            "void",
-                            Collections.singletonList("java.lang.String[]")))) {
-          mainMethods.add(method);
-        }
-      }
-    }
+    Collection<SootMethod> mainMethods =
+        view.getClasses()
+            .filter(aClass -> !aClass.isLibraryClass())
+            .flatMap(aClass -> aClass.getMethods().stream())
+            .filter(
+                method ->
+                    method.isStatic()
+                        && JavaIdentifierFactory.getInstance()
+                            .isMainSubSignature(method.getSignature().getSubSignature()))
+            .collect(Collectors.toSet());
 
     if (mainMethods.size() > 1) {
       throw new RuntimeException(
diff --git a/sootup.core/src/main/java/sootup/core/views/View.java b/sootup.core/src/main/java/sootup/core/views/View.java
index 90298498163..14c80c51339 100644
--- a/sootup.core/src/main/java/sootup/core/views/View.java
+++ b/sootup.core/src/main/java/sootup/core/views/View.java
@@ -22,8 +22,8 @@
  * #L%
  */
 
-import java.util.Collection;
 import java.util.Optional;
+import java.util.stream.Stream;
 import javax.annotation.Nonnull;
 import sootup.core.IdentifierFactory;
 import sootup.core.model.SootClass;
@@ -44,7 +44,7 @@ public interface View {
 
   /** Return all classes in the view. */
   @Nonnull
-  Collection<? extends SootClass> getClasses();
+  Stream<? extends SootClass> getClasses();
 
   /**
    * Return a class with given signature.
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/RuntimeJarConversionTests.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/RuntimeJarConversionTests.java
index 18110fc5ef3..63b933f07cc 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/RuntimeJarConversionTests.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/RuntimeJarConversionTests.java
@@ -34,7 +34,7 @@ public void testJarWithDefaultInterceptors() {
 
   private static void convertInputLocation(AnalysisInputLocation inputLocation) {
     JavaView view = new JavaView(Collections.singletonList(inputLocation));
-    long classesCount = view.getClasses().size();
+    long classesCount = view.getClasses().count();
     if (debug) {
       System.out.println("classes: " + classesCount);
     }
@@ -42,7 +42,7 @@ private static void convertInputLocation(AnalysisInputLocation inputLocation) {
     long[] progress = {0};
 
     long count =
-        view.getClasses().stream()
+        view.getClasses()
             .peek(
                 c -> {
                   if (!debug) {
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1577Test.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1577Test.java
index 364ed101d28..606cee291d1 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1577Test.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1577Test.java
@@ -26,8 +26,8 @@ public void test() {
 
     JavaView view = new JavaView(inputLocation);
 
-    assertEquals(1, view.getClasses().size());
+    assertEquals(1, view.getClasses().count());
 
-    view.getClasses().stream().findFirst().get().getMethods().forEach(SootMethod::getBody);
+    view.getClasses().findFirst().get().getMethods().forEach(SootMethod::getBody);
   }
 }
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1580Test.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1580Test.java
index 1ae14d0d56e..2237e2e9f29 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1580Test.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/Soot1580Test.java
@@ -29,7 +29,7 @@ public void test() {
 
     JavaView view = new JavaView(Collections.singletonList(inputLocation));
 
-    assertEquals(91, view.getClasses().size());
+    assertEquals(91, view.getClasses().count());
 
     ClassType clazzType =
         JavaIdentifierFactory.getInstance().getClassType("cn.jpush.android.data.f");
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/MultiReleaseJarAnalysisInputLocationTest.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/MultiReleaseJarAnalysisInputLocationTest.java
index d822c17c910..545a37cd77e 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/MultiReleaseJarAnalysisInputLocationTest.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/MultiReleaseJarAnalysisInputLocationTest.java
@@ -148,7 +148,8 @@ public void multiReleaseJar() {
 
     // getClasses
     List<String> collectedClassesWPrintBody9 =
-        view_9.getClasses().stream()
+        view_9
+            .getClasses()
             .map(c -> c.getMethod(printBodyMethodSubSig))
             .filter(Optional::isPresent)
             .map(m -> m.get().getBody().toString())
@@ -157,7 +158,8 @@ public void multiReleaseJar() {
     assertTrue(collectedClassesWPrintBody9.get(0).contains("java 9"));
 
     List<String> collectedClassesWPrintBody10 =
-        view_10.getClasses().stream()
+        view_10
+            .getClasses()
             .map(c -> c.getMethod(printBodyMethodSubSig))
             .filter(Optional::isPresent)
             .map(m -> m.get().getBody().toString())
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/PathBasedAnalysisInputLocationTest.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/PathBasedAnalysisInputLocationTest.java
index 29b03486384..49f59bc2e9e 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/PathBasedAnalysisInputLocationTest.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/PathBasedAnalysisInputLocationTest.java
@@ -123,7 +123,7 @@ public void testClassInWar() {
     // Get the view
     JavaView view = new JavaView(new JavaClassPathAnalysisInputLocation(warFile));
 
-    assertEquals(19, view.getClasses().size());
+    assertEquals(19, view.getClasses().count());
 
     // Create java class signature
     ClassType utilsClassSignature = view.getIdentifierFactory().getClassType("Employee", "ds");
@@ -215,11 +215,7 @@ public void testInputLocationLibraryMode() {
 
     Collection<SootClass> classes = new HashSet<>(); // Set to track the classes to check
 
-    for (SootClass aClass : view.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
+    view.getClasses().filter(aClass -> !aClass.isLibraryClass()).forEach(classes::add);
 
     assertEquals(0, classes.size(), "User Defined class found, expected none");
   }
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/RandomJarTest.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/RandomJarTest.java
index e0d7101b855..6d8207f0bba 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/RandomJarTest.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/inputlocation/RandomJarTest.java
@@ -6,6 +6,7 @@
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.Collection;
+import java.util.stream.Collectors;
 import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
 import sootup.core.inputlocation.AnalysisInputLocation;
@@ -99,7 +100,7 @@ public void writeTestMetrics(TestMetrics testMetrics) {
 
   private Collection<JavaSootClass> getClasses(JavaView view) {
     try {
-      return view.getClasses();
+      return view.getClasses().collect(Collectors.toList());
     } catch (Exception e) {
       throw new RuntimeException("Error while getting class list", e);
     }
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/AggregatorTest.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/AggregatorTest.java
index eec8aa1b219..a845dcba242 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/AggregatorTest.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/AggregatorTest.java
@@ -194,8 +194,7 @@ public void testIssue739() {
     final ClassType classType = view.getIdentifierFactory().getClassType("Issue739_Aggregator");
     assertTrue(view.getClass(classType).isPresent());
 
-    for (JavaSootMethod javaSootMethod :
-        view.getClasses().stream().findFirst().get().getMethods()) {
+    for (JavaSootMethod javaSootMethod : view.getClasses().findFirst().get().getMethods()) {
       final Body body = javaSootMethod.getBody();
     }
   }
@@ -215,8 +214,7 @@ public void testIssue911() {
     final ClassType classType = view.getIdentifierFactory().getClassType("Issue911_Aggregator");
     assertTrue(view.getClass(classType).isPresent());
 
-    for (JavaSootMethod javaSootMethod :
-        view.getClasses().stream().findFirst().get().getMethods()) {
+    for (JavaSootMethod javaSootMethod : view.getClasses().findFirst().get().getMethods()) {
       final Body body = javaSootMethod.getBody();
     }
   }
diff --git a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/LocalSplitterTest.java b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/LocalSplitterTest.java
index 0c4dac0332b..5c647256004 100644
--- a/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/LocalSplitterTest.java
+++ b/sootup.java.bytecode/src/test/java/sootup/java/bytecode/interceptors/LocalSplitterTest.java
@@ -60,7 +60,7 @@ public void JRT() {
 
     // ~200_000 methods
     view.getClasses()
-        .parallelStream()
+        .parallel()
         .flatMap(clazz -> clazz.getMethods().stream())
         .filter(method -> !method.isAbstract() && !method.isNative())
         .forEach(SootMethod::getBody);
diff --git a/sootup.java.core/src/main/java/sootup/java/core/views/JavaView.java b/sootup.java.core/src/main/java/sootup/java/core/views/JavaView.java
index 8afe18bc4af..5add98e949e 100644
--- a/sootup.java.core/src/main/java/sootup/java/core/views/JavaView.java
+++ b/sootup.java.core/src/main/java/sootup/java/core/views/JavaView.java
@@ -22,11 +22,10 @@
  * #L%
  */
 
-import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
-import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import javax.annotation.Nonnull;
 import sootup.core.cache.ClassCache;
 import sootup.core.cache.FullCache;
@@ -82,20 +81,17 @@ protected JavaView(
   /** Resolves all classes that are part of the view and stores them in the cache. */
   @Override
   @Nonnull
-  public synchronized Collection<JavaSootClass> getClasses() {
+  public synchronized Stream<JavaSootClass> getClasses() {
     if (isFullyResolved && cache instanceof FullCache) {
-      return cache.getClasses().stream()
-          .map(clazz -> (JavaSootClass) clazz)
-          .collect(Collectors.toList());
+      return cache.getClasses().stream().map(clazz -> (JavaSootClass) clazz);
     }
 
-    Collection<JavaSootClass> resolvedClasses =
+    Stream<JavaSootClass> resolvedClasses =
         inputLocations.stream()
             .flatMap(location -> location.getClassSources(this).stream())
             .map(this::buildClassFrom)
             .filter(Optional::isPresent)
-            .map(Optional::get)
-            .collect(Collectors.toList());
+            .map(Optional::get);
 
     isFullyResolved = true;
 
diff --git a/sootup.java.core/src/test/java/sootup/java/core/views/JavaViewTest.java b/sootup.java.core/src/test/java/sootup/java/core/views/JavaViewTest.java
index 23dfc9b6f39..0f5821607f1 100644
--- a/sootup.java.core/src/test/java/sootup/java/core/views/JavaViewTest.java
+++ b/sootup.java.core/src/test/java/sootup/java/core/views/JavaViewTest.java
@@ -2,10 +2,10 @@
 
 import static org.junit.jupiter.api.Assertions.*;
 
-import java.util.Collection;
 import java.util.Comparator;
 import java.util.List;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Tag;
@@ -71,12 +71,12 @@ public void testResolveUndefinedClassAfterAllResolved() {
 
   @Disabled
   public void testResolveAll() {
-    Collection<JavaSootClass> classes = this.view.getClasses();
+    Stream<JavaSootClass> classes = this.view.getClasses();
 
-    assertEquals(classes.size(), this.signatures.size());
+    assertEquals(classes.count(), this.signatures.size());
 
     assertEquals(
-        classes.stream()
+        classes
             .map(AbstractClass::getType)
             .sorted(Comparator.comparing(Type::toString))
             .collect(Collectors.toList()),
diff --git a/sootup.java.sourcecode/src/test/java/sootup/java/sourcecode/inputlocation/JavaSourcePathNamespaceTest.java b/sootup.java.sourcecode/src/test/java/sootup/java/sourcecode/inputlocation/JavaSourcePathNamespaceTest.java
index eb2f5620666..183f29b8bc7 100644
--- a/sootup.java.sourcecode/src/test/java/sootup/java/sourcecode/inputlocation/JavaSourcePathNamespaceTest.java
+++ b/sootup.java.sourcecode/src/test/java/sootup/java/sourcecode/inputlocation/JavaSourcePathNamespaceTest.java
@@ -62,7 +62,7 @@ public void testGetClassSources() {
     final JavaView view = new JavaView(inputLocation);
 
     Collection<? extends AbstractClassSource> classSources =
-        view.getClasses().stream().map(jsc -> jsc.getClassSource()).collect(Collectors.toList());
+        view.getClasses().map(jsc -> jsc.getClassSource()).collect(Collectors.toList());
 
     ClassType type = new JavaClassType("Array1", PackageName.DEFAULT_PACKAGE);
     Optional<ClassType> optionalFoundType =
@@ -91,11 +91,7 @@ public void testInputSourcePathLibraryMode() {
     JavaView view = new JavaView(inputLocation);
 
     Set<SootClass> classes = new HashSet<>(); // Set to track the classes to check
-    for (SootClass aClass : view.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
+    view.getClasses().filter(aClass -> !aClass.isLibraryClass()).forEach(classes::add);
 
     assertEquals(0, classes.size(), "User Defined class found, expected none");
   }
diff --git a/sootup.jimple.parser/src/main/java/sootup/jimple/parser/JimpleView.java b/sootup.jimple.parser/src/main/java/sootup/jimple/parser/JimpleView.java
index 17a964b742c..5d07861501b 100644
--- a/sootup.jimple.parser/src/main/java/sootup/jimple/parser/JimpleView.java
+++ b/sootup.jimple.parser/src/main/java/sootup/jimple/parser/JimpleView.java
@@ -27,6 +27,7 @@
 import java.util.List;
 import java.util.Optional;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import javax.annotation.Nonnull;
 import sootup.core.IdentifierFactory;
 import sootup.core.cache.ClassCache;
@@ -77,8 +78,8 @@ public JimpleView(
 
   @Override
   @Nonnull
-  public synchronized Collection<SootClass> getClasses() {
-    return getAbstractClassSources();
+  public synchronized Stream<SootClass> getClasses() {
+    return getAbstractClassSources().stream();
   }
 
   @Nonnull
diff --git a/sootup.qilin/src/main/java/qilin/core/PTAScene.java b/sootup.qilin/src/main/java/qilin/core/PTAScene.java
index 97fee24201d..8ea9ecad168 100644
--- a/sootup.qilin/src/main/java/qilin/core/PTAScene.java
+++ b/sootup.qilin/src/main/java/qilin/core/PTAScene.java
@@ -95,13 +95,11 @@ public SootMethod getMethod(String methodSignature) {
   }
 
   public Collection<SootClass> getApplicationClasses() {
-    Collection<? extends SootClass> classes = view.getClasses();
-    return classes.stream().filter(SootClass::isApplicationClass).collect(Collectors.toSet());
+    return view.getClasses().filter(SootClass::isApplicationClass).collect(Collectors.toSet());
   }
 
   public Collection<SootClass> getLibraryClasses() {
-    Collection<? extends SootClass> classes = view.getClasses();
-    return classes.stream().filter(SootClass::isLibraryClass).collect(Collectors.toSet());
+    return view.getClasses().filter(SootClass::isLibraryClass).collect(Collectors.toSet());
   }
 
   public boolean containsMethod(String methodSignature) {
@@ -117,7 +115,7 @@ public boolean containsField(String fieldSignature) {
   }
 
   public Collection<? extends SootClass> getClasses() {
-    return view.getClasses();
+    return view.getClasses().collect(Collectors.toList());
   }
 
   public Collection<SootClass> getPhantomClasses() {
diff --git a/sootup.qilin/src/main/java/qilin/core/VirtualCalls.java b/sootup.qilin/src/main/java/qilin/core/VirtualCalls.java
index ac4d39f5618..1c8a4f3e68c 100644
--- a/sootup.qilin/src/main/java/qilin/core/VirtualCalls.java
+++ b/sootup.qilin/src/main/java/qilin/core/VirtualCalls.java
@@ -44,7 +44,7 @@ public class VirtualCalls {
 
   public VirtualCalls(View view) {
     this.view = view;
-    this.typeToVtbl = DataFactory.createMap(view.getClasses().size());
+    this.typeToVtbl = DataFactory.createMap((int) view.getClasses().count());
   }
 
   public SootMethod resolveSpecial(
diff --git a/sootup.qilin/src/main/java/qilin/core/builder/CallGraphBuilder.java b/sootup.qilin/src/main/java/qilin/core/builder/CallGraphBuilder.java
index e388732bb69..8bb391570df 100644
--- a/sootup.qilin/src/main/java/qilin/core/builder/CallGraphBuilder.java
+++ b/sootup.qilin/src/main/java/qilin/core/builder/CallGraphBuilder.java
@@ -72,7 +72,7 @@ public CallGraphBuilder(PTA pta) {
     this.ptaScene = pta.getScene();
     ptaScene.setCallGraph(new OnFlyCallGraph());
     this.virtualCalls = new VirtualCalls(ptaScene.getView());
-    receiverToSites = DataFactory.createMap(ptaScene.getView().getClasses().size());
+    receiverToSites = DataFactory.createMap((int) ptaScene.getView().getClasses().count());
     methodToInvokeStmt = DataFactory.createMap();
     reachMethods = DataFactory.createSet();
     calledges = DataFactory.createSet();
diff --git a/sootup.qilin/src/main/java/qilin/core/builder/ExceptionHandler.java b/sootup.qilin/src/main/java/qilin/core/builder/ExceptionHandler.java
index 986efabc42f..86622921b43 100644
--- a/sootup.qilin/src/main/java/qilin/core/builder/ExceptionHandler.java
+++ b/sootup.qilin/src/main/java/qilin/core/builder/ExceptionHandler.java
@@ -40,7 +40,7 @@ public class ExceptionHandler {
   public ExceptionHandler(PTA pta) {
     this.pta = pta;
     this.pag = pta.getPag();
-    this.throwNodeToSites = DataFactory.createMap(pta.getView().getClasses().size());
+    this.throwNodeToSites = DataFactory.createMap((int) pta.getView().getClasses().count());
   }
 
   public Collection<ExceptionThrowSite> throwSitesLookUp(VarNode throwNode) {
diff --git a/sootup.qilin/src/main/java/qilin/core/builder/FakeMainFactory.java b/sootup.qilin/src/main/java/qilin/core/builder/FakeMainFactory.java
index faa7846ca95..05ec0e96f23 100644
--- a/sootup.qilin/src/main/java/qilin/core/builder/FakeMainFactory.java
+++ b/sootup.qilin/src/main/java/qilin/core/builder/FakeMainFactory.java
@@ -20,7 +20,6 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.Iterator;
@@ -348,10 +347,7 @@ public List<SootMethod> all() {
     /** Returns a list of all static initializers. */
     public List<SootMethod> clinits() {
       List<SootMethod> ret = new ArrayList<>();
-      Collection<? extends SootClass> classes = view.getClasses();
-      for (SootClass cl : classes) {
-        addMethod(ret, cl, sigClinit);
-      }
+      view.getClasses().forEach(cl -> addMethod(ret, cl, sigClinit));
       return ret;
     }
 
diff --git a/sootup.qilin/src/main/java/qilin/stat/CallGraphStat.java b/sootup.qilin/src/main/java/qilin/stat/CallGraphStat.java
index eeaffa6692e..8ba33912909 100644
--- a/sootup.qilin/src/main/java/qilin/stat/CallGraphStat.java
+++ b/sootup.qilin/src/main/java/qilin/stat/CallGraphStat.java
@@ -18,7 +18,6 @@
 
 package qilin.stat;
 
-import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Set;
@@ -31,7 +30,6 @@
 import qilin.core.pag.ContextMethod;
 import qilin.core.pag.ContextVarNode;
 import qilin.core.pag.LocalVarNode;
-import sootup.core.model.SootClass;
 import sootup.core.model.SootMethod;
 
 public class CallGraphStat implements AbstractStat {
@@ -70,10 +68,8 @@ public CallGraphStat(PTA pta) {
 
   private void init() {
     // stat method numbers
-    Collection<? extends SootClass> clazzs = pta.getView().getClasses();
-    for (SootClass clazz : clazzs) {
-      allMethods += clazz.getMethods().size();
-    }
+    allMethods +=
+        pta.getView().getClasses().map(clazz -> clazz.getMethods().size()).reduce(0, Integer::sum);
     //
     OnFlyCallGraph csCallGraph = pta.getCgb().getCallGraph();
     CSCallEdges = csCallGraph.size();
diff --git a/sootup.tests/src/test/java/sootup/tests/CacheTest.java b/sootup.tests/src/test/java/sootup/tests/CacheTest.java
index a7dd764ade1..843bac497c0 100644
--- a/sootup.tests/src/test/java/sootup/tests/CacheTest.java
+++ b/sootup.tests/src/test/java/sootup/tests/CacheTest.java
@@ -49,7 +49,7 @@ public void fullCacheTest() {
     view.getClass(utilsOperationClassType);
     assertEquals(2, view.getCachedClassesCount());
 
-    view.getClasses();
+    view.getClasses().count();
     assertEquals(6, view.getCachedClassesCount());
   }
 
@@ -72,7 +72,7 @@ public void lruCacheTest() {
     assertEquals(1, view.getCachedClassesCount());
 
     JavaView newView = new JavaView(inputLocations, new LRUCacheProvider());
-    newView.getClasses();
+    newView.getClasses().count();
     assertEquals(6, newView.getCachedClassesCount());
   }
 }
diff --git a/sootup.tests/src/test/java/sootup/tests/MutableSootClientTest.java b/sootup.tests/src/test/java/sootup/tests/MutableSootClientTest.java
index 4ceb62d1483..7633b063720 100644
--- a/sootup.tests/src/test/java/sootup/tests/MutableSootClientTest.java
+++ b/sootup.tests/src/test/java/sootup/tests/MutableSootClientTest.java
@@ -54,10 +54,10 @@ public void setupMutableView() {
    */
   @Test
   public void classRemovalTest() {
-    int classesBeforeSize = mv.getClasses().size();
+    long classesBeforeSize = mv.getClasses().count();
     ClassType classType = mv.getIdentifierFactory().getClassType("utils.Operations");
     mv.removeClass(classType);
-    int classesAfterSize = mv.getClasses().size();
+    long classesAfterSize = mv.getClasses().count();
 
     assertEquals(classesBeforeSize, classesAfterSize + 1);
   }
@@ -85,9 +85,9 @@ public void classAdditionTest() {
             Collections.emptySet(),
             Collections.emptySet());
 
-    int classesBeforeSize = mv.getClasses().size();
+    long classesBeforeSize = mv.getClasses().count();
     mv.addClass(newClass.buildClass(SourceType.Application));
-    int classesAfterSize = mv.getClasses().size();
+    long classesAfterSize = mv.getClasses().count();
 
     assertEquals(classesBeforeSize, classesAfterSize - 1);
   }
diff --git a/sootup.tests/src/test/java/sootup/tests/validator/CheckInitValidatorTest.java b/sootup.tests/src/test/java/sootup/tests/validator/CheckInitValidatorTest.java
index 4da64924568..4ac3dd4a507 100644
--- a/sootup.tests/src/test/java/sootup/tests/validator/CheckInitValidatorTest.java
+++ b/sootup.tests/src/test/java/sootup/tests/validator/CheckInitValidatorTest.java
@@ -60,11 +60,7 @@ public PackageName getPackageName() {
 
     classes = new HashSet<>(); // Set to track the classes to check
 
-    for (SootClass aClass : jimpleView.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
+    jimpleView.getClasses().forEach(classes::add);
   }
 
   @Test
diff --git a/sootup.tests/src/test/java/sootup/tests/validator/FieldRefValidatorTest.java b/sootup.tests/src/test/java/sootup/tests/validator/FieldRefValidatorTest.java
index c9a8da0826f..ba9493f275c 100644
--- a/sootup.tests/src/test/java/sootup/tests/validator/FieldRefValidatorTest.java
+++ b/sootup.tests/src/test/java/sootup/tests/validator/FieldRefValidatorTest.java
@@ -61,11 +61,7 @@ public PackageName getPackageName() {
 
     classes = new HashSet<>(); // Set to track the classes to check
 
-    for (SootClass aClass : jimpleView.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
+    jimpleView.getClasses().forEach(classes::add);
   }
 
   @Test
diff --git a/sootup.tests/src/test/java/sootup/tests/validator/LocalsValidatorTest.java b/sootup.tests/src/test/java/sootup/tests/validator/LocalsValidatorTest.java
index 468f060a900..524b33f70f8 100644
--- a/sootup.tests/src/test/java/sootup/tests/validator/LocalsValidatorTest.java
+++ b/sootup.tests/src/test/java/sootup/tests/validator/LocalsValidatorTest.java
@@ -59,11 +59,7 @@ public PackageName getPackageName() {
 
     classes = new HashSet<>(); // Set to track the classes to check
 
-    for (SootClass aClass : jimpleView.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
+    jimpleView.getClasses().forEach(classes::add);
   }
 
   @Test
diff --git a/sootup.tests/src/test/java/sootup/tests/validator/NewValidatorTest.java b/sootup.tests/src/test/java/sootup/tests/validator/NewValidatorTest.java
index 5b7a573bb3b..83b3b4cbc8a 100644
--- a/sootup.tests/src/test/java/sootup/tests/validator/NewValidatorTest.java
+++ b/sootup.tests/src/test/java/sootup/tests/validator/NewValidatorTest.java
@@ -61,11 +61,7 @@ public PackageName getPackageName() {
 
     classes = new HashSet<>(); // Set to track the classes to check
 
-    for (SootClass aClass : view.getClasses()) {
-      if (!aClass.isLibraryClass()) {
-        classes.add(aClass);
-      }
-    }
+    view.getClasses().forEach(classes::add);
   }
 
   @Test