Add a jinstance method for checking Java type

ctrueden · ctrueden · commit bc8be7659c7a · 2022-11-02T22:34:59.000-05:00
diff --git a/src/scyjava/__init__.py b/src/scyjava/__init__.py
@@ -102,6 +102,7 @@
     jarray,
     jclass,
     jimport,
+    jinstance,
     jstacktrace,
     jvm_started,
     jvm_version,
diff --git a/src/scyjava/_convert.py b/src/scyjava/_convert.py
@@ -8,7 +8,7 @@
 
 from jpype import JArray, JBoolean, JByte, JChar, JDouble, JFloat, JInt, JLong, JShort
 
-from ._java import JavaClasses, isjava, jclass, jimport, start_jvm
+from ._java import JavaClasses, isjava, jclass, jimport, jinstance, start_jvm
 
 
 # NB: We cannot use org.scijava.priority.Priority or other Java-side class
@@ -681,7 +681,7 @@ def _import_numpy(required=True):
 def _is_table(obj: Any) -> bool:
     """Check if obj is a table."""
     try:
-        return isinstance(obj, jimport("org.scijava.table.Table"))
+        return jinstance(obj, "org.scijava.table.Table")
     except BaseException:
         # No worries if scijava-table is not available.
         pass
diff --git a/src/scyjava/_java.py b/src/scyjava/_java.py
@@ -384,6 +384,20 @@ def jclass(data):
     raise TypeError("Cannot glean class from data of type: " + str(type(data)))
 
 
+def jinstance(obj, jtype):
+    """
+    Test if the given object is an instance of a particular Java type.
+
+    :param obj: The object to check.
+    :param jtype: The Java type, as either a jimported class or as a string.
+    :returns: True iff the object is an instance of that Java type.
+    """
+    if isinstance(jtype, str):
+        jtype = jimport(jtype)
+
+    return isinstance(obj, jtype)
+
+
 def jstacktrace(exc):
     """
     Extract the Java-side stack trace from a Java exception.
diff --git a/tests/test_convert.py b/tests/test_convert.py
@@ -3,7 +3,16 @@
 
 from jpype import JByte
 
-from scyjava import Converter, config, jarray, jclass, jimport, to_java, to_python
+from scyjava import (
+    Converter,
+    config,
+    jarray,
+    jclass,
+    jimport,
+    jinstance,
+    to_java,
+    to_python,
+)
 
 config.endpoints.append("org.scijava:scijava-table")
 config.add_option("-Djava.awt.headless=true")
@@ -182,7 +191,7 @@ def testDict(self):
     def testPath(self):
         py_path = Path(getcwd())
         j_path = to_java(py_path)
-        assert isinstance(j_path, jimport("java.nio.file.Path"))
+        assert jinstance(j_path, "java.nio.file.Path")
         assert str(j_path) == str(py_path)
 
         actual = to_python(j_path)
diff --git a/tests/test_pandas.py b/tests/test_pandas.py
@@ -2,7 +2,7 @@
 import numpy.testing as npt
 import pandas as pd
 
-from scyjava import config, jimport, to_java
+from scyjava import config, jinstance, to_java
 
 config.endpoints.append("org.scijava:scijava-table")
 config.add_option("-Djava.awt.headless=true")
@@ -28,8 +28,7 @@ def testPandasToTable(self):
         table = to_java(df)
 
         assert_same_table(table, df)
-        DefaultFloatTable = jimport("org.scijava.table.DefaultFloatTable")
-        assert isinstance(table, DefaultFloatTable)
+        assert jinstance(table, "org.scijava.table.DefaultFloatTable")
 
         # Int table.
         columns = ["header1", "header2", "header3", "header4", "header5"]
@@ -40,8 +39,7 @@ def testPandasToTable(self):
         table = to_java(df)
 
         assert_same_table(table, df)
-        DefaultIntTable = jimport("org.scijava.table.DefaultIntTable")
-        assert isinstance(table, DefaultIntTable)
+        assert jinstance(table, "org.scijava.table.DefaultIntTable")
 
         # Bool table.
         columns = ["header1", "header2", "header3", "header4", "header5"]
@@ -51,8 +49,7 @@ def testPandasToTable(self):
         table = to_java(df)
 
         assert_same_table(table, df)
-        DefaultBoolTable = jimport("org.scijava.table.DefaultBoolTable")
-        assert isinstance(table, DefaultBoolTable)
+        assert jinstance(table, "org.scijava.table.DefaultBoolTable")
 
         # Mixed table.
         columns = ["header1", "header2", "header3", "header4", "header5"]
@@ -71,5 +68,4 @@ def testPandasToTable(self):
 
         # Table types cannot be the same here, unless we want to cast.
         # assert_same_table(table, df)
-        DefaultGenericTable = jimport("org.scijava.table.DefaultGenericTable")
-        assert isinstance(table, DefaultGenericTable)
+        assert jinstance(table, "org.scijava.table.DefaultGenericTable")
