fixed incorrect checking string equality

Author: epidemia

aima-core/src/main/java/aima/core/environment/connectfour/ConnectFourGame.java

@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 
 import aima.core.search.adversarial.Game;
 
@@ -54,7 +55,7 @@ public String getPlayer(int playerNum) {
 	 */
 	public int getPlayerNum(String player) {
 		for (int i = 0; i < players.length; i++)
-			if (players[i] == player)
+			if (Objects.equals(players[i], player))
 				return i+1;
 		throw new IllegalArgumentException("Wrong player number.");
 	}
@@ -84,7 +85,7 @@ public boolean isTerminal(ConnectFourState state) {
 	public double getUtility(ConnectFourState state, String player) {
 		double result = state.getUtility();
 		if (result != -1) {
-			if (player == players[1])
+			if (Objects.equals(player, players[1]))
 				result = 1 - result;
 		} else {
 			throw new IllegalArgumentException("State is not terminal.");

aima-core/src/main/java/aima/core/environment/tictactoe/TicTacToeGame.java

@@ -1,6 +1,7 @@
 package aima.core.environment.tictactoe;
 
 import java.util.List;
+import java.util.Objects;
 
 import aima.core.search.adversarial.Game;
 import aima.core.util.datastructure.XYLocation;
@@ -52,7 +53,7 @@ public boolean isTerminal(TicTacToeState state) {
 	public double getUtility(TicTacToeState state, String player) {
 		double result = state.getUtility();
 		if (result != -1) {
-			if (player == TicTacToeState.O)
+			if (Objects.equals(player, TicTacToeState.O))
 				result = 1 - result;
 		} else {
 			throw new IllegalArgumentException("State is not terminal.");

aima-gui/src/main/java/aima/gui/fx/views/MapEnvironmentViewCtrl.java

@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 
 import aima.core.agent.Agent;
 import aima.core.agent.Environment;
@@ -78,7 +79,7 @@ protected void update() {
 			// print track of first agent
 			if (!env.getAgents().isEmpty()) {
 				String aLoc = env.getAgentLocation(env.getAgents().get(0));
-				if (track.isEmpty() || track.get(track.size() - 1) != aLoc)
+				if (track.isEmpty() || !Objects.equals(track.get(track.size() - 1), aLoc))
 					track.add(aLoc);
 				for (int i = 1; i < track.size(); i++) {
 					Point2D pt1 = map.getPosition(track.get(i - 1));