Remove unneeded empty string concatentation

This commit removes concatenation by empty string in places where it
is simply not needed to obtain a string representation.

Relates #24411

core/src/main/java/org/elasticsearch/index/engine/Segment.java

@@ -284,7 +284,7 @@ public class Segment implements Streamable {
                 out.writeBoolean(((SortedNumericSortField) field).getSelector() == SortedNumericSelector.Type.MAX);
                 out.writeBoolean(field.getReverse());
             } else {
-                throw new IOException("invalid index sort field:" + field + "");
+                throw new IOException("invalid index sort field:" + field);
             }
         }
     }

core/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -399,7 +399,7 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
             currentRouting = this.shardRouting;
 
             if (!newRouting.shardId().equals(shardId())) {
-                throw new IllegalArgumentException("Trying to set a routing entry with shardId " + newRouting.shardId() + " on a shard with shardId " + shardId() + "");
+                throw new IllegalArgumentException("Trying to set a routing entry with shardId " + newRouting.shardId() + " on a shard with shardId " + shardId());
             }
             if ((currentRouting == null || newRouting.isSameAllocation(currentRouting)) == false) {
                 throw new IllegalArgumentException("Trying to set a routing entry with a different allocation. Current " + currentRouting + ", new " + newRouting);

core/src/main/java/org/elasticsearch/repositories/RepositoryData.java

@@ -210,7 +210,7 @@ public final class RepositoryData {
     public Set<SnapshotId> getSnapshots(final IndexId indexId) {
         Set<SnapshotId> snapshotIds = indexSnapshots.get(indexId);
         if (snapshotIds == null) {
-            throw new IllegalArgumentException("unknown snapshot index " + indexId + "");
+            throw new IllegalArgumentException("unknown snapshot index " + indexId);
         }
         return snapshotIds;
     }

core/src/main/java/org/elasticsearch/search/lookup/LeafDocLookup.java

@@ -76,7 +76,7 @@ public class LeafDocLookup implements Map<String, ScriptDocValues<?>> {
         if (scriptValues == null) {
             final MappedFieldType fieldType = mapperService.fullName(fieldName);
             if (fieldType == null) {
-                throw new IllegalArgumentException("No field found for [" + fieldName + "] in mapping with types " + Arrays.toString(types) + "");
+                throw new IllegalArgumentException("No field found for [" + fieldName + "] in mapping with types " + Arrays.toString(types));
             }
             // load fielddata on behalf of the script: otherwise it would need additional permissions
             // to deal with pagedbytes/ramusagestimator/etc

core/src/main/java/org/elasticsearch/search/lookup/LeafFieldsLookup.java

@@ -135,7 +135,7 @@ public class LeafFieldsLookup implements Map {
         if (data == null) {
             MappedFieldType fieldType = mapperService.fullName(name);
             if (fieldType == null) {
-                throw new IllegalArgumentException("No field found for [" + name + "] in mapping with types " + Arrays.toString(types) + "");
+                throw new IllegalArgumentException("No field found for [" + name + "] in mapping with types " + Arrays.toString(types));
             }
             data = new FieldLookup(fieldType);
             cachedFieldData.put(name, data);

core/src/main/java/org/elasticsearch/snapshots/SnapshotShardsService.java

@@ -497,7 +497,7 @@ public class SnapshotShardsService extends AbstractLifecycleComponent implements
 
         @Override
         public String toString() {
-            return "" + snapshot + ", shardId [" + shardId + "], status [" + status.state() + "]";
+            return snapshot + ", shardId [" + shardId + "], status [" + status.state() + "]";
         }
     }
 

core/src/main/java/org/elasticsearch/transport/TcpTransport.java

@@ -684,7 +684,7 @@ public abstract class TcpTransport<Channel> extends AbstractLifecycleComponent i
         try {
             hostAddresses = networkService.resolveBindHostAddresses(bindHosts);
         } catch (IOException e) {
-            throw new BindTransportException("Failed to resolve host " + Arrays.toString(bindHosts) + "", e);
+            throw new BindTransportException("Failed to resolve host " + Arrays.toString(bindHosts), e);
         }
         if (logger.isDebugEnabled()) {
             String[] addresses = new String[hostAddresses.length];

modules/lang-painless/src/main/java/org/elasticsearch/painless/DefMath.java

@@ -379,8 +379,10 @@ public class DefMath {
     }
     
     private static Object add(Object left, Object right) {
-        if (left instanceof String || right instanceof String) {
+        if (left instanceof String) {
-            return "" + left + right;
+            return (String) left + right;
+        } else if (right instanceof String) {
+            return left + (String) right;
         } else if (left instanceof Number) {
             if (right instanceof Number) {
                 if (left instanceof Double || right instanceof Double) {

modules/lang-painless/src/main/java/org/elasticsearch/painless/node/EBinary.java

@@ -291,7 +291,7 @@ public final class EBinary extends AExpression {
             } else if (sort == Sort.DOUBLE) {
                 constant = (double)left.constant + (double)right.constant;
             } else if (sort == Sort.STRING) {
-                constant = "" + left.constant + right.constant;
+                constant = left.constant.toString() + right.constant.toString();
             } else {
                 throw createError(new IllegalStateException("Illegal tree structure."));
             }

test/framework/src/main/java/org/elasticsearch/search/aggregations/metrics/AbstractNumericTestCase.java

@@ -39,7 +39,7 @@ public abstract class AbstractNumericTestCase extends ESIntegTestCase {
 
         final int numDocs = 10;
         for (int i = 0; i < numDocs; i++) { // TODO randomize the size and the params in here?
-            builders.add(client().prepareIndex("idx", "type", ""+i).setSource(jsonBuilder()
+            builders.add(client().prepareIndex("idx", "type", String.valueOf(i)).setSource(jsonBuilder()
                     .startObject()
                     .field("value", i+1)
                     .startArray("values").value(i+2).value(i+3).endArray()
@@ -58,7 +58,7 @@ public abstract class AbstractNumericTestCase extends ESIntegTestCase {
         prepareCreate("empty_bucket_idx").addMapping("type", "value", "type=integer").execute().actionGet();
         builders = new ArrayList<>();
         for (int i = 0; i < 2; i++) {
-            builders.add(client().prepareIndex("empty_bucket_idx", "type", ""+i).setSource(jsonBuilder()
+            builders.add(client().prepareIndex("empty_bucket_idx", "type", String.valueOf(i)).setSource(jsonBuilder()
                     .startObject()
                     .field("value", i*2)
                     .endObject()));

test/framework/src/main/java/org/elasticsearch/test/disruption/NetworkDisruption.java

@@ -110,7 +110,7 @@ public class NetworkDisruption implements ServiceDisruptionScheme {
 
     protected void ensureNodeCount(InternalTestCluster cluster) {
         assertFalse("cluster failed to form after disruption was healed", cluster.client().admin().cluster().prepareHealth()
-            .setWaitForNodes("" + cluster.size())
+            .setWaitForNodes(String.valueOf(cluster.size()))
             .setWaitForNoRelocatingShards(true)
             .get().isTimedOut());
     }

test/framework/src/main/java/org/elasticsearch/test/disruption/SingleNodeDisruption.java

@@ -84,7 +84,7 @@ public abstract class SingleNodeDisruption implements ServiceDisruptionScheme {
 
     protected void ensureNodeCount(InternalTestCluster cluster) {
         assertFalse("cluster failed to form after disruption was healed", cluster.client().admin().cluster().prepareHealth()
-                .setWaitForNodes("" + cluster.size())
+                .setWaitForNodes(String.valueOf(cluster.size()))
                 .setWaitForNoRelocatingShards(true)
                 .get().isTimedOut());
     }