JUnit Testing: It throws java.lang.NullPointerException when testing a pair of String related setter and getter

Question

here is my class that needed to test:

public class RankingTableModel {

/**
 * filePath stores the path of a csv file.
 */
private String filePath = "";

/**
 * table data represents all the data in the table cells.
 */
private Object[][] table_data;

public String getFilePath () {
    return filePath;
}

public void setFilePath (String filePath) {
    this.filePath = filePath;
}

here is my JUnit test class (for @Before, @After, .etc, I didn't do any thing special, just print some messages):

public class RankingTableModelTest {

private static final Object[][] data = {
            {"US", new Integer(1), new Integer(2), new Integer(2),
                new Integer(3)},
            {"UK", new Integer(2), new Integer(2), new Integer(1),
                new Integer(2)},
            {"CHN", new Integer(3), new Integer(1), new Integer(3),
                new Integer(1)},
        };

private static final String file_path = "test";

private RankingTableModel test_model;


@Test
public void setFilePathAndGetFilePath() {

    System.out.println("Testing setFilePath and getFilePath.");
    test_model.setFilePath(file_path);
    assertEquals(test_model.getFilePath(),"test");
}

}

When I run the test, it throws an exception: java.lang.NullPointerException at * .RankingTableModelTest.setFilePathAndGetFilePath(RankingTableModelTest.java:51) 51 is the number of line : test_model.setFilePath(file_path);

What is the problem with my code? Thx :)

Answer 1

You never instantiated test_model .

Somewhere, you'll need test_model = new RankingTableModel(); or something similar.

Answer 2

You have just declared test_model:

private RankingTableModel test_model;

Not, initialized it.

private RankingTableModel test_model = new RankingTableModel();

Above line will fix your problem.