导入org.junit.Assert时出错

Question

I'm having a little problem with a unit-test my professor gave me. Upon compilation, I recieve the following errors:
cannot find symbol import org.junit.Assert.assertArrayEquals; cannot find symbol import org.junit.Assert.assertEquals; import org.junit.Assert.assertFalse; import org.junit.Assert.assertTrue;

I have downloaded JUnit and I can compile a similar file, so why am I having problems with this? The code is:

import java.util.Comparator;
import org.junit.Assert.assertArrayEquals;
import org.junit.Assert.assertEquals;
import org.junit.Assert.assertFalse;
import org.junit.Assert.assertTrue;
import org.junit.Before;
import org.junit.Test;

    public class SortingTests {

      class IntegerComparator implements Comparator<Integer> {
        @Override
        public int compare(Integer i1, Integer i2) {
          return i1.compareTo(i2);
        }
      }

      private Integer i1,i2,i3;
      private OrderedArray<Integer> orderedArray;

      @Before
      public void createOrderedArray(){
        i1 = -12;
        i2 = 0;
        i3 = 4;
        orderedArray = new OrderedArray<>(new IntegerComparator());
      }

      @Test
      public void testIsEmpty_zeroEl(){
        assertTrue(orderedArray.isEmpty());
      }

      @Test
      public void testIsEmpty_oneEl() throws Exception{
        orderedArray.add(i1);
        assertFalse(orderedArray.isEmpty());
      }


      @Test
      public void testSize_zeroEl() throws Exception{
        assertEquals(0,orderedArray.size());
      }

    }

Answer 1

Assuming that you have the JUnit dependency in the classpath, use import static for the assert methods:

import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

Or simply use:

import static org.junit.Assert.*;

Answer 2

You should add the keyword static to import it. An example:

 import static org.junit.Assert.assertFalse;

Answer 3

What you are looking for is a Static import

The line import org.junit.Assert.assertArrayEquals; is referencing the method assertArrayEquals from the class org.junit.Assert

Importing a static method so that it is callable like assertEquals(0,orderedArray.size()); is done with a static import line. Try out the following:

import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

Alternatively you can:

import static org.junit.Assert.*;

, or you could:

import org.junit.Assert;

and reference the methods like

Assert.assertEquals(0,orderedArray.size());