# Accessing C++ Switches In Java [TOC] ## Introduction Accessing C++ switches in Java is implemented via a Python script which analyzes the C++ switches file and generates the corresponding Java class, based on a template file. The template file must be specified in the GN target. ## Usage 1. Create a template file (ex. `FooSwitches.java.tmpl`). Change "Copyright 2020" to be whatever the year is at the time of writing (as you would for any other file). ```java // Copyright 2020 The Chromium Authors. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. package org.chromium.foo; // Be sure to escape any curly braces in your template by doubling as // follows. /** * Contains command line switches that are specific to the foo project. */ public final class FooSwitches {{ {NATIVE_STRINGS} // Prevents instantiation. private FooSwitches() {{}} }} ``` 2. Add a new build target and add it to the `srcjar_deps` of an `android_library` target: ```gn if (is_android) { import("//build/config/android/rules.gni") } if (is_android) { java_cpp_strings("java_switches_srcjar") { # External code should depend on ":foo_java" instead. visibility = [ ":*" ] sources = [ "//base/android/foo_switches.cc", ] template = "//base/android/java_templates/FooSwitches.java.tmpl" } # If there's already an android_library target, you can add # java_switches_srcjar to that target's srcjar_deps. Otherwise, the best # practice is to create a new android_library just for this target. android_library("foo_java") { srcjar_deps = [ ":java_switches_srcjar" ] } } ``` 3. The generated file `out/Default/gen/.../org/chromium/foo/FooSwitches.java` would contain: ```java // Copyright $YEAR The Chromium Authors. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. package org.chromium.foo; /** * Contains command line switches that are specific to the foo project. */ public final class FooSwitches { // ...snip... // This following string constants were inserted by // java_cpp_strings.py // From // ../../base/android/foo_switches.cc // Into // ../../base/android/java_templates/FooSwitches.java.tmpl // Documentation for the C++ switch is copied here. public static final String SOME_SWITCH = "some-switch"; // ...snip... // Prevents instantiation. private FooSwitches() {} } ``` ## See also * [Accessing C++ Enums In Java](android_accessing_cpp_enums_in_java.md) * [Accessing C++ Features In Java](android_accessing_cpp_features_in_java.md) ## Code * [Generator code](https://cs.chromium.org/chromium/src/build/android/gyp/java_cpp_strings.py?dr=C&sq=package:chromium) and [Tests](https://cs.chromium.org/chromium/src/build/android/gyp/java_cpp_strings_tests.py?dr=C&sq=package:chromium) * [GN template](https://cs.chromium.org/chromium/src/build/config/android/rules.gni?sq=package:chromium&dr=C)