Thread: Sorting an array without using the method sort()

Hi guys,

I'm a beginner in Java. I need to sort a set of grades from students and print them sorted together with the index they occupy in the input vector. I've done the following:

 
package edu.uoc.pac1;
 
public class PAC1Ex3 {
 
public static void sortAverageGradesAndShowIndices(double[] averageNotes) {
       double doubleNotes, aux;
        for (int i=0; i < averageNotes.length -1; i++){
            for (int j=0; j < averageNotes.length -1; j++){
                // If actual number is higher than next one
                if(averageNotes[j] > averageNotes[j+1]){
                    // Swapping 
                    aux = averageNotes[j];
                    averageNotes[j] = averageNotes[j+1];
                    averageNotes[j+1]=aux;
                }
            }
        }
        // Print numbers sorted 
        for (int i=(averageNotes.length-1); i>=0;i--){
            System.out.println((averageNotes[i]));
        }
    }
}

I'm at the same time trying to test if it works with the following code:

 
package edu.uoc.pac1;
 
class PAC1Ex3Test {
 
@Test
@Order(4)
void testSortAverageNotesAndShowIndices() {
 
        ByteArrayOutputStream outputStreamCaptor = new ByteArrayOutputStream();
        System.setOut(new PrintStream(outputStreamCaptor));
        PAC1Ex3.sortAverageGradesAndShowIndices(new double[] {4.2, 8.1, 9.4, 6.1, 4.7, 6.4, 6.0, 7.7});
        assertEquals("9.4 (2)"+System.lineSeparator()
                + "8.1 (1)"+System.lineSeparator()
                + "7.7 (7)"+System.lineSeparator()
                + "6.4 (5)"+System.lineSeparator()
                + "6.1 (3)"+System.lineSeparator()
                + "6.0 (6)"+System.lineSeparator()
                + "4.7 (4)"+System.lineSeparator()
                + "4.2 (0)", outputStreamCaptor.toString().trim());
 
        outputStreamCaptor = new ByteArrayOutputStream();
        System.setOut(new PrintStream(outputStreamCaptor));
        PAC1Ex3.sortAverageGradesAndShowIndices(new double[] {6.6, 7.9, 8.9, 9.6, 7.3, 6.5, 4.0});
        assertEquals("9.6 (3)"+System.lineSeparator()
                + "8.9 (2)"+System.lineSeparator()
                + "7.9 (1)"+System.lineSeparator()
                + "7.3 (4)"+System.lineSeparator()
                + "6.6 (0)"+System.lineSeparator()
                + "6.5 (5)"+System.lineSeparator()
                + "4.0 (6)", outputStreamCaptor.toString().trim());
 
 
        outputStreamCaptor = new ByteArrayOutputStream();
        System.setOut(new PrintStream(outputStreamCaptor));
        PAC1Ex3.sortAverageGradesAndShowIndices(new double[] {7.0, 7.5, 8.0, 8.5, 9.0});
        assertEquals("9.0 (4)"+System.lineSeparator()
                + "8.5 (3)"+System.lineSeparator()
                + "8.0 (2)"+System.lineSeparator()
                + "7.5 (1)"+System.lineSeparator()
                + "7.0 (0)", outputStreamCaptor.toString().trim());
 
 
    }
}

However, my actual output is the following one:

9.4
8.1
7.7
6.4
6.1
6.0
4.7
4.2

I'm missing the original position.

 
org.opentest4j.AssertionFailedError: 
<Click to see difference>
 
 
	at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
	at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
	at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
	at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1124)
	at edu.uoc.pac1.PAC1Ex3Test.testSortAverageNotesAndShowIndices(PAC1Ex3Test.java:106)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:564)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
	at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
	at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
	at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
	at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
	at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:210)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
	at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
 
 
Process finished with exit code -1

I'm getting AssertionFailedError.

Where is that error message from? Can you copy the full contents of the console from when the code is executed and paste it here?

How can a tester compile and execute the code? It is not complete; the posted code can not be compiled. It needs import statements, a class definition and a main method.


Can you print out the results from the sort and compare it against the desired output to see what is wrong?

Have you printed out the results of the sortAverageGradesAndShowIndices method?
Does the contents of that print out look ok?

Add a print statement at the end of the method that prints out the contents of the array:

System.out.println("an ID "+ java.util.Arrays.toString(theArrayName)); //<<  change theArrayName to the correct name

I'm getting the following:

Ok, does that look like the correct results? It does not look like it is sorted.

I'm missing the position of the numbers from the source vector.

So, you need to make some more changes to the code.
Can you use a custom class to hold the item's value and its initial position in the array?

Create a class to hold the double number and the int initial index. Create a new array.
For each double number in the original array, create an instance of the class with its double value and its int index number.
Save that instance in the new array.
Sort the objects in the new array based on the double value in the instance. Moving the instance around will always keep the double value paired with its int value.