New J2K: Add JavaStandardMethodsConversion

j2k/newSrc/org/jetbrains/kotlin/j2k/conversions/JavaMethodToKotlinFunctionConversion.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.j2k.conversions
 
 import org.jetbrains.kotlin.j2k.ConversionContext
+import org.jetbrains.kotlin.j2k.ast.Nullability
 import org.jetbrains.kotlin.j2k.throwAnnotation
 import org.jetbrains.kotlin.j2k.tree.*
 import org.jetbrains.kotlin.j2k.tree.impl.JKKtFunctionImpl
@@ -35,9 +36,11 @@ class JavaMethodToKotlinFunctionConversion(private val context: ConversionContex
                 declaration.invalidate()
 
                 JKKtFunctionImpl(
-                    JKTypeElementImpl(
-                        declaration.returnType.type.updateNullability(declaration.returnTypeNullability(context))
-                    ),
+                    if (declaration.returnType.type.nullability != Nullability.NotNull)
+                        JKTypeElementImpl(
+                            declaration.returnType.type
+                                .updateNullability(declaration.returnTypeNullability(context))
+                        ) else declaration.returnType,
                     declaration.name,
                     declaration.parameters,
                     declaration.block,

j2k/newSrc/org/jetbrains/kotlin/j2k/conversions/JavaStandartMethodsConversion.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.j2k.conversions
+
+import org.jetbrains.kotlin.j2k.ast.Nullability
+import org.jetbrains.kotlin.j2k.tree.*
+import org.jetbrains.kotlin.j2k.tree.impl.JKJavaMethodImpl
+import org.jetbrains.kotlin.j2k.tree.impl.JKTypeElementImpl
+
+class JavaStandartMethodsConversion : RecursiveApplicableConversionBase() {
+    override fun applyToElement(element: JKTreeElement): JKTreeElement {
+        if (element !is JKJavaMethodImpl) return recurse(element)
+        if (fixToStringMethod(element)) {
+            return recurse(element)
+        }
+        return recurse(element)
+    }
+
+    private fun fixToStringMethod(method: JKJavaMethodImpl): Boolean {
+        if (method.name.value != "toString") return false
+        if (method.parameters.isNotEmpty()) return false
+        val type = (method.returnType.type as? JKClassType)
+            ?.takeIf { it.classReference.name == "String" }
+            ?.updateNullability(Nullability.NotNull) ?: return false
+        method.returnType = JKTypeElementImpl(type)
+        return true
+    }
+}

j2k/newSrc/org/jetbrains/kotlin/j2k/tree/jk.kt

@@ -88,7 +88,7 @@ interface JKMethod : JKDeclaration, JKVisibilityOwner, JKModalityOwner, JKExtraM
     JKAnnotationListOwner {
     val name: JKNameIdentifier
     var parameters: List<JKParameter>
-    val returnType: JKTypeElement
+    var returnType: JKTypeElement
     var block: JKBlock
 }