java: Fix tests when CBC not available

examples/contrib/Issue173.java

@@ -14,8 +14,11 @@ public class Issue173 {
   }
 
   private static void solveLP() {
-    MPSolver solver =
-        new MPSolver("test", MPSolver.OptimizationProblemType.CBC_MIXED_INTEGER_PROGRAMMING);
+    MPSolver solver = MPSolver.createSolver("CBC");
+    if (solver == null) {
+      System.out.println("Could not create solver CBC");
+      return;
+    }
     MPVariable x = solver.makeNumVar(Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY, "x");
 
     final MPObjective objective = solver.objective();

examples/contrib/KnapsackMIP.java

@@ -26,17 +26,12 @@ import com.google.ortools.Loader;
 import com.google.ortools.linearsolver.*;
 
 public class KnapsackMIP {
-  private static MPSolver createSolver(String solverType) {
-    try {
-      return new MPSolver("MIPDiet", MPSolver.OptimizationProblemType.valueOf(solverType));
-    } catch (java.lang.IllegalArgumentException e) {
-      System.err.println("Bad solver type: " + e);
-      return null;
-    }
-  }
-
   private static void solve(String solverType) {
-    MPSolver solver = createSolver(solverType);
+    MPSolver solver = MPSolver.createSolver(solverType);
+    if (solver == null) {
+      System.out.println("Could not create solver");
+      return;
+    }
 
     /** variables */
     int itemCount = 12;

examples/contrib/MultiThreadTest.java

@@ -63,8 +63,11 @@ public class MultiThreadTest {
   }
 
   private static MPSolver makeProblem() {
-    MPSolver solver = new MPSolver(
-        UUID.randomUUID().toString(), OptimizationProblemType.CBC_MIXED_INTEGER_PROGRAMMING);
+    MPSolver solver = MPSolver.createSolver("CBC");
+    if (solver == null) {
+      System.out.println("Could not create solver CBC");
+      return solver;
+    }
 
     double infinity = MPSolver.infinity();
 
@@ -97,11 +100,14 @@ public class MultiThreadTest {
     @Override
     public ResultStatus call() throws Exception {
       MPSolver solver = makeProblem();
-      statusSolver = solver.solve();
-
-      // Check that the problem has an optimal solution.
-      if (MPSolver.ResultStatus.OPTIMAL.equals(statusSolver)) {
-        throw new RuntimeException("Non OPTIMAL status after solve.");
+      if (solver == null) {
+        statusSolver = MPSolver.ResultStatus.NOT_SOLVED;
+      } else {
+        statusSolver = solver.solve();
+        // Check that the problem has an optimal solution.
+        if (MPSolver.ResultStatus.OPTIMAL.equals(statusSolver)) {
+          throw new RuntimeException("Non OPTIMAL status after solve.");
+        }
       }
       return statusSolver;
     }