Modernized: Replaced Collections.emptyList() with List.of() and deprecated singletonList(T) and singletonSet(T)

Author: mkarg

src/main/java/com/beust/jcommander/converters/CommaParameterSplitter.java

@@ -1,11 +1,10 @@
 package com.beust.jcommander.converters;
 
-import java.util.Collections;
 import java.util.List;
 
 public class CommaParameterSplitter implements IParameterSplitter {
 
   public List<String> split(String value) {
-    return value.isEmpty() ? Collections.emptyList() : List.of(value.split(","));
+    return value.isEmpty() ? List.of() : List.of(value.split(","));
   }
 }

src/test/java/com/beust/jcommander/DefaultValueTest.java

@@ -87,8 +87,8 @@ public static class MyOpts {
 
   public static final class MyOptsWithDefaultValues extends MyOpts {
     public MyOptsWithDefaultValues(){
-      this.list = singletonList("defaultValue");
-      this.set = singletonSet("defaultValue");
+      this.list = List.of("defaultValue");
+      this.set = Set.of("defaultValue");
     }
   }
 
@@ -99,12 +99,14 @@ public MyOptsWithEmptyDefaults(){
     }
   }
 
+  @Deprecated(forRemoval = true, since = "4.0")
   public static final List<String> singletonList(String value) {
     List<String> list = Lists.newArrayList();
     list.add(value);
     return list;
   }
 
+  @Deprecated(forRemoval = true, since = "4.0")
   public static final Set<String> singletonSet(String value){
     Set<String> set = Sets.newLinkedHashSet();
     set.add(value);
@@ -115,7 +117,7 @@ public static final Set<String> singletonSet(String value){
   public void missingRequiredParameterWithDefaultValueShouldNotRaiseParameterException() {
     class MyRequiredOptsWithDefaultValues {
       @Parameter(names = "-a", required = true)
-      public List<String> list = singletonList("defaultValue");
+      public List<String> list = List.of("defaultValue");
     }
 
     MyRequiredOptsWithDefaultValues opts = new MyRequiredOptsWithDefaultValues();

src/test/java/com/beust/jcommander/ListOfPathTest.java

@@ -4,7 +4,6 @@
 import org.testng.annotations.Test;
 
 import java.nio.file.Path;
-import java.util.Collections;
 import java.util.List;
 
 public class ListOfPathTest {
@@ -14,7 +13,7 @@ public void testParse() {
         // given
         final class Args {
             @Parameter(names = { "--paths"}, description = "List of paths separated by comma")
-            private List<Path> paths = Collections.emptyList();
+            private List<Path> paths = List.of();
         }
         final Args args = new Args();
 

src/test/java/com/beust/jcommander/converters/CommaParameterSplitterTest.java

@@ -1,6 +1,5 @@
 package com.beust.jcommander.converters;
 
-import java.util.Collections;
 import java.util.List;
 
 import org.testng.Assert;
@@ -14,13 +13,13 @@ public class CommaParameterSplitterTest {
   @Test
   public void testSplit() {
     // An empty string becomes an empty list.
-    Assert.assertEquals(Collections.emptyList(), SPLITTER.split(""));
+    Assert.assertEquals(List.of(), SPLITTER.split(""));
 
     // Whitespace is unaltered.
-    Assert.assertEquals(Collections.singletonList("  "), SPLITTER.split("  "));
+    Assert.assertEquals(List.of("  "), SPLITTER.split("  "));
 
     // Single value.
-    Assert.assertEquals(Collections.singletonList("abc"), SPLITTER.split("abc"));
+    Assert.assertEquals(List.of("abc"), SPLITTER.split("abc"));
 
     // Multiple values.
     Assert.assertEquals(List.of("a", "b", "c"), SPLITTER.split("a,b,c"));