ICU-23054 Fix all Errorprone complaints at error level

Author: mihnita

icu4j/main/charset/src/test/java/com/ibm/icu/dev/test/charset/TestCharset.java

@@ -5818,7 +5818,8 @@ public void TestBufferOverflowErrorUsingJavagetBytes() {
         String testCase = "\u7d42";
 
         try {
-            testCase.getBytes(charsetName);
+            // We don't expect any particular value.
+            var unused = testCase.getBytes(charsetName);
         } catch (Exception ex) {
             errln("Error calling getBytes(): " + ex);
         }

icu4j/main/collate/src/test/java/com/ibm/icu/dev/test/collator/CollationAPITest.java

@@ -313,7 +313,7 @@ public void TestElemIter() {
 
         // Code coverage for dummy "not designed" hashCode() which does "assert false".
         try {
-            iterator1.hashCode();  // We don't expect any particular value.
+            var unused = iterator1.hashCode();  // We don't expect any particular value.
         } catch (AssertionError ignored) {
             // Expected to be thrown if assertions are enabled.
         }

icu4j/main/core/src/main/java/com/ibm/icu/impl/UnicodeMap.java

@@ -857,6 +857,7 @@ public UnicodeMap<T> putAll(Map<? extends String, ? extends T> map) {
      * Utility for extracting map
      * @deprecated
      */
+    @Deprecated
     public UnicodeMap<T> putAllIn(Map<? super String, ? super T> map) {
         for (String key : keySet()) {
             map.put(key, get(key));

icu4j/main/core/src/test/java/com/ibm/icu/dev/test/TestBoilerplate.java

@@ -39,6 +39,7 @@ public abstract class TestBoilerplate<T> extends TestFmwk {
 
     protected static Random random = new Random(12345);
 
+    @SuppressWarnings({"SelfEquals", "EqualsNull"})
     protected final void _test() throws Exception {
         List<T> list = new LinkedList<T>();
         while (_addTestObject(list)) {

icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/APIInfo.java

@@ -80,7 +80,7 @@ public boolean equals(Object rhs) {
                 this.name.equals(that.name) &&
                 this.sig.equals(that.sig) &&
                 this.exc.equals(that.exc) &&
-                this.stver.equals(this.stver);
+                this.stver.equals(that.stver);
         }
         catch (ClassCastException e) {
             return false;

icu4j/tools/misc/src/main/java/com/ibm/icu/dev/tool/charsetdet/mbcs/BIG5Tool.java

@@ -234,7 +234,7 @@ void processDir(File dir) {
     //  WARNING:  this class's natural ordering (from Comparable) and equals()
     //            are inconsistent.
 
-    static class ChEl implements Comparable {
+    static class ChEl implements Comparable<ChEl> {
         int charCode;
         int occurences;
 
@@ -258,10 +258,9 @@ public int hashCode() {
 
         // We want to be able to sort the results by frequency of occurrence
         //   Compare backwards.  We want most frequent chars first.
-        public int compareTo(Object other) {
-            ChEl o = (ChEl)other;
-            return (this.occurences> o.occurences? -1 :
-                   (this.occurences==o.occurences?  0 : 1));
+        public int compareTo(ChEl other) {
+            return (this.occurences> other.occurences? -1 :
+                   (this.occurences==other.occurences?  0 : 1));
         }
 
     }

icu4j/tools/misc/src/main/java/com/ibm/icu/dev/tool/charsetdet/mbcs/EUCTool.java

@@ -234,7 +234,7 @@ void processDir(File dir) {
     //  WARNING:  this class's natural ordering (from Comparable) and equals()
     //            are inconsistent.
 
-    static class ChEl implements Comparable {
+    static class ChEl implements Comparable<ChEl> {
         int charCode;
         int occurences;
 
@@ -258,10 +258,9 @@ public int hashCode() {
 
         // We want to be able to sort the results by frequency of occurrence
         //   Compare backwards.  We want most frequent chars first.
-        public int compareTo(Object other) {
-            ChEl o = (ChEl)other;
-            return (this.occurences> o.occurences? -1 :
-                   (this.occurences==o.occurences?  0 : 1));
+        public int compareTo(ChEl other) {
+            return (this.occurences> other.occurences? -1 :
+                   (this.occurences==other.occurences?  0 : 1));
         }
 
     }

icu4j/tools/misc/src/main/java/com/ibm/icu/dev/tool/charsetdet/sbcs/NGramList.java

@@ -26,7 +26,7 @@ public interface NGramKeyMapper
         Object mapKey(String key);
     }
 
-    public static final class NGram implements Comparable
+    public static final class NGram implements Comparable<NGram>
     {
         private String value;
         private int refCount;
@@ -63,11 +63,9 @@ public final void incrementRefCount()
         }
 
         // Note: This makes higher refCounts come *before* lower refCounts...
-        public int compareTo(Object o)
+        public int compareTo(NGram o)
         {
-            NGram ng = (NGram) o;
-            
-            return ng.getRefCount() - refCount;
+            return o.getRefCount() - refCount;
         }
     }