diff --git a/java/java-psi-impl/src/com/intellij/psi/impl/source/PsiJavaFileBaseImpl.java b/java/java-psi-impl/src/com/intellij/psi/impl/source/PsiJavaFileBaseImpl.java
index 241d47d0e2e3..cd5e45b9d56b 100644
--- a/java/java-psi-impl/src/com/intellij/psi/impl/source/PsiJavaFileBaseImpl.java
+++ b/java/java-psi-impl/src/com/intellij/psi/impl/source/PsiJavaFileBaseImpl.java
@@ -27,7 +27,9 @@ import com.intellij.psi.impl.java.stubs.PsiJavaFileStub;
 import com.intellij.psi.impl.source.resolve.ClassResolverProcessor;
 import com.intellij.psi.impl.source.resolve.SymbolCollectingProcessor;
 import com.intellij.psi.impl.source.resolve.SymbolCollectingProcessor.ResultWithContext;
+import com.intellij.psi.impl.source.tree.FileElement;
 import com.intellij.psi.impl.source.tree.JavaElementType;
+import com.intellij.psi.impl.source.tree.TreeUtil;
 import com.intellij.psi.scope.*;
 import com.intellij.psi.scope.processor.MethodsProcessor;
 import com.intellij.psi.stubs.StubElement;
@@ -618,31 +620,36 @@ public abstract class PsiJavaFileBaseImpl extends PsiFileImpl implements PsiJava
     if (virtualFile == null) virtualFile = getViewProvider().getVirtualFile();
 
     String sourceLevel = null;
-    try {
-      CharSequence contents = getViewProvider().getContents();
-      int lineBound = Strings.indexOf(contents, "\n");
-      CharSequence line = lineBound > 0 ? contents.subSequence(0, lineBound) : contents;
-      if (Strings.startsWith(line, 0,"#!")) {
-        List<String> params = ParametersListUtil.parse(line.toString());
-        int srcIdx = params.indexOf("--source");
-        if (srcIdx > 0 && srcIdx + 1 < params.size()) {
-          sourceLevel = params.get(srcIdx + 1);
-          LanguageLevel sheBangLevel = LanguageLevel.parse(sourceLevel);
-          if (sheBangLevel != null) {
-            return sheBangLevel;
+    FileElement treeElement = getTreeElement();
+    ASTNode firstLeaf = treeElement == null ? null : TreeUtil.findFirstLeaf(treeElement, false);
+    // optimization: do not (re)compute the whole file text on each PSI change - will lead to quadratic nightmare in case of many small changes otherwise
+    if (firstLeaf == null || Strings.startsWith(firstLeaf.getChars(), 0, "#!")) {
+      try {
+        CharSequence contents = getViewProvider().getContents();
+        int lineBound = Strings.indexOf(contents, "\n");
+        CharSequence line = lineBound > 0 ? contents.subSequence(0, lineBound) : contents;
+        if (Strings.startsWith(line, 0, "#!")) {
+          List<String> params = ParametersListUtil.parse(line.toString());
+          int srcIdx = params.indexOf("--source");
+          if (srcIdx > 0 && srcIdx + 1 < params.size()) {
+            sourceLevel = params.get(srcIdx + 1);
+            LanguageLevel sheBangLevel = LanguageLevel.parse(sourceLevel);
+            if (sheBangLevel != null) {
+              return sheBangLevel;
+            }
           }
         }
       }
-    }
-    catch (Throwable ignored) {
-    }
-    finally {
-      if (!Objects.equals(sourceLevel, virtualFile.getUserData(SHEBANG_SOURCE_LEVEL)) && virtualFile.isInLocalFileSystem()) {
-        virtualFile.putUserData(SHEBANG_SOURCE_LEVEL, sourceLevel);
-        VirtualFile file = virtualFile;
-        ApplicationManager.getApplication().invokeLater(() -> FileContentUtilCore.reparseFiles(file),
-                                                        ModalityState.nonModal(),
-                                                        ApplicationManager.getApplication().getDisposed());
+      catch (Throwable ignored) {
+      }
+      finally {
+        if (!Objects.equals(sourceLevel, virtualFile.getUserData(SHEBANG_SOURCE_LEVEL)) && virtualFile.isInLocalFileSystem()) {
+          virtualFile.putUserData(SHEBANG_SOURCE_LEVEL, sourceLevel);
+          VirtualFile file = virtualFile;
+          ApplicationManager.getApplication().invokeLater(() -> FileContentUtilCore.reparseFiles(file),
+                                                          ModalityState.nonModal(),
+                                                          ApplicationManager.getApplication().getDisposed());
+        }
       }
     }
 
diff --git a/java/java-tests/testSrc/com/intellij/psi/impl/PsiModificationStressTest.java b/java/java-tests/testSrc/com/intellij/psi/impl/PsiModificationStressTest.java
new file mode 100644
index 000000000000..5bae27259c67
--- /dev/null
+++ b/java/java-tests/testSrc/com/intellij/psi/impl/PsiModificationStressTest.java
@@ -0,0 +1,24 @@
+// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.psi.impl;
+
+import com.intellij.psi.PsiClass;
+import com.intellij.psi.PsiElementFactory;
+import com.intellij.psi.PsiField;
+import com.intellij.testFramework.LightJavaCodeInsightTestCase;
+
+public class PsiModificationStressTest extends LightJavaCodeInsightTestCase {
+  public void testManySmallPSIChangesDoNotCauseQuadraticRecomputationsOfWholeFileText() {
+    int N = 100_000;
+    String text = "  int field;\n".repeat(N);
+
+    PsiClass aClass = PsiElementFactory.getInstance(getProject()).createClassFromText(text, null);
+    assertFalse(aClass.isPhysical());
+    PsiField firstField = aClass.getFields()[0];
+    // would pass only if each PSI change does not cause recomputation of the whole file text in com.intellij.psi.impl.source.PsiJavaFileBaseImpl.getLanguageLevelInner
+    for (int i = 0; i < N; i++) {
+      firstField.setName("f" + i);
+    }
+    assertFalse(aClass.isPhysical());
+    assertEquals(N, aClass.getFields().length);
+  }
+}