Cache indentation spaces lazily in JavaOutput.

core/src/main/java/com/google/googlejavaformat/java/JavaFormatterOptions.java

@@ -69,7 +69,7 @@ public int tabWidth() {
     /** Returns the indentation string for the given visual column width. */
     public String indentString(int indent) {
       if (!useTabs()) {
-        return " ".repeat(indent);
+        return JavaOutput.spaces(indent);
       }
       int tabWidth = tabWidth();
       return "\t".repeat(indent / tabWidth) + " ".repeat(indent % tabWidth);

core/src/main/java/com/google/googlejavaformat/java/JavaOutput.java

@@ -62,14 +62,32 @@ public final class JavaOutput extends Output {
   private StringBuilder lineBuilder = new StringBuilder();
   private StringBuilder spacesPending = new StringBuilder();
 
+  private static final int MAX_CACHED_SPACES = 100;
+  private static final String[] spaces = new String[MAX_CACHED_SPACES + 1];
+
+  /** Returns an indentation string of the given number of spaces. */
+  static String spaces(int indent) {
+    if (indent <= 0) {
+      return "";
+    }
+    if (indent <= MAX_CACHED_SPACES) {
+      String result = spaces[indent];
+      if (result == null) {
+        result = spaces[indent] = " ".repeat(indent);
+      }
+      return result;
+    }
+    return " ".repeat(indent);
+  }
+
   /**
    * {@code JavaOutput} constructor.
    *
    * @param javaInput the {@link Input}, used to match up blank lines in the output
    * @param commentsHelper the {@link CommentsHelper}, used to rewrite comments
    */
   public JavaOutput(String lineSeparator, Input javaInput, CommentsHelper commentsHelper) {
-    this(lineSeparator, javaInput, commentsHelper, indent -> " ".repeat(Math.max(0, indent)));
+    this(lineSeparator, javaInput, commentsHelper, JavaOutput::spaces);
   }
 
   /**

core/src/test/java/com/google/googlejavaformat/java/FormatterTest.java

@@ -829,6 +829,12 @@ public void styleVisualLengthAndIndentString() {
     assertThat(google.indentString(0)).isEmpty();
     assertThat(googleTabs.indentString(0)).isEmpty();
     assertThat(aospTabs.indentString(0)).isEmpty();
+    assertThat(google.indentString(4)).isSameInstanceAs(google.indentString(4));
+    assertThat(google.indentString(104)).isEqualTo(" ".repeat(104));
+    assertThat(googleTabs.indentString(104)).isEqualTo("\t".repeat(52));
+    assertThat(JavaOutput.spaces(4)).isSameInstanceAs(JavaOutput.spaces(4));
+    assertThat(JavaOutput.spaces(0)).isEmpty();
+    assertThat(JavaOutput.spaces(104)).isEqualTo(" ".repeat(104));
   }
 
   @Test