Fix support for 'class' properties in Java codegen (#4237)

* Fix support for 'class' properties in Java codegen

Currently Java codegen works successfully for property named 'class' but
fails on '_class', '__class', etc, because of 'Object.getClass()'
overloading.

This fix is intended to avoid all Object method overloading cases.

* Regenerated samples for Java petstore-security-test

samples/client/petstore/java/jersey2-java8/docs/ClassModel.md

@@ -0,0 +1,10 @@
+
+# ClassModel
+
+## Properties
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**propertyClass** | **String** |  |  [optional]
+
+
+

samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ClassModel.java

@@ -0,0 +1,90 @@
+/*
+ * Swagger Petstore
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * OpenAPI spec version: 1.0.0
+ * Contact: apiteam@swagger.io
+ *
+ * NOTE: This class is auto generated by the swagger code generator program.
+ * https://github.com/swagger-api/swagger-codegen.git
+ * Do not edit the class manually.
+ */
+
+
+package io.swagger.client.model;
+
+import java.util.Objects;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import io.swagger.annotations.ApiModel;
+import io.swagger.annotations.ApiModelProperty;
+
+/**
+ * Model for testing model with \"_class\" property
+ */
+@ApiModel(description = "Model for testing model with \"_class\" property")
+
+public class ClassModel {
+  @JsonProperty("_class")
+  private String propertyClass = null;
+
+  public ClassModel propertyClass(String propertyClass) {
+    this.propertyClass = propertyClass;
+    return this;
+  }
+
+   /**
+   * Get propertyClass
+   * @return propertyClass
+  **/
+  @ApiModelProperty(example = "null", value = "")
+  public String getPropertyClass() {
+    return propertyClass;
+  }
+
+  public void setPropertyClass(String propertyClass) {
+    this.propertyClass = propertyClass;
+  }
+
+
+  @Override
+  public boolean equals(java.lang.Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    ClassModel classModel = (ClassModel) o;
+    return Objects.equals(this.propertyClass, classModel.propertyClass);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(propertyClass);
+  }
+
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class ClassModel {\n");
+    
+    sb.append("    propertyClass: ").append(toIndentedString(propertyClass)).append("\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(java.lang.Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+  
+}
+