Steps to reproduce:
1) run the following example using Java 7 and again using Java 8:
{code:java}
import java.util.ArrayList;
import java.util.List;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.ColumnConstraints;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

public class BetpalFXApplication extends Application {

 

    @Override
    public void start(Stage stage) throws Exception {
        GridPane root = createGrid();
        stage.setScene(new Scene(root));
        stage.show();
    }

 

    private GridPane createGrid() {
        BorderPane left = new BorderPane();
        left.setStyle("-fx-background-color: red");
        left.setCenter(new Label("left"));
        BorderPane middle = new BorderPane();
        middle.setStyle("-fx-background-color: yellow");
        middle.setCenter(new Label("middle"));
        BorderPane right = new BorderPane();
        right.setStyle("-fx-background-color: blue");
        right.setCenter(new Label("right"));

        GridPane root = new GridPane();
        double[] widthPercentColumnConstraintsThree = { 33.3, 33.3, 33.3 };
        setColumnConstraints(root, widthPercentColumnConstraintsThree);
        root.add(left, 0, 0);
        root.add(middle, 1, 0);
        root.add(right, 2, 0);
        return root;
    }

 

    private void setColumnConstraints(GridPane gridPane, double[] widthPercentColumnConstraints) {

        List<ColumnConstraints> listOfColumnConstraints = new ArrayList<ColumnConstraints>();

        for (double widthPercentColumnConstraint : widthPercentColumnConstraints) {

            ColumnConstraints columnConstraints = new ColumnConstraints();

            columnConstraints.setPercentWidth(widthPercentColumnConstraint);

            listOfColumnConstraints.add(columnConstraints);

        }

        gridPane.getColumnConstraints().setAll(listOfColumnConstraints);

    }

 

    public static void main(String[] args) {

        Application.launch(args);

    }

}
{code}

Expected result:
We can see the same result using both Java 7 and 8 which is a small window containing colorful grid pane with 3 equal size columns.

Actual result:
We see the expected result for Java 7 and very wide window in Java 8.

Notes:
We know that 33.3 + 33.3 + 33.3 != 100 but it worked in Java 7.
Using { 33.3, 33.3, 33.4 } usually helps BUT in some cases if you use { 33.3, 33.4, 33.3 } it doesn't work even though it's sum is 100. ( see https://community.oracle.com/thread/3537869 )