BAEL-1530 - Guide to java.lang.System (#3616)

* Different types of bean injection in Spring - eval

* Different types of bean injection in Spring - eval - changed to java config

* Different types of bean injection in Spring - eval - unit tests and fixes

* BAEL-1530 - Guide to java.lang.System

* removed eval article stuff

* updated unit tests: removed sysouts and unrelated stuff

* updated examples for easiness. refactoring.

* fixed typos, identified by unit tests

* broken into multiple unit tests

core-java/src/test/java/com/baeldung/system/DateTimeServiceTest.java

@@ -0,0 +1,15 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class DateTimeServiceTest {
+
+    @Test
+    public void givenClass_whenCalledMethods_thenNotNullInResult() {
+        DateTimeService dateTimeService = new DateTimeService();
+
+        Assert.assertNotNull(dateTimeService.nowPlusOneHour());
+        Assert.assertNotNull(dateTimeService.nowPrettyPrinted());
+    }
+}

core-java/src/test/java/com/baeldung/system/EnvironmentVariablesTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class EnvironmentVariablesTest {
+
+    @Test
+    public void givenEnvVars_whenReadPath_thenGetValueinResult() {
+        EnvironmentVariables environmentVariables = new EnvironmentVariables();
+
+        Assert.assertNotNull(environmentVariables.getPath());
+    }
+}

core-java/src/test/java/com/baeldung/system/SystemArrayCopyTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SystemArrayCopyTest {
+
+    @Test
+    public void givenTwoArraysAB_whenUseArrayCopy_thenArrayCopiedFromAToBInResult() {
+        int[] a = {34, 22, 44, 2, 55, 3};
+        int[] b = new int[a.length];
+
+        // copy all elements from a to b
+        System.arraycopy(a, 0, b, 0, a.length);
+        Assert.assertArrayEquals(a, b);
+    }
+
+    @Test
+    public void givenTwoArraysAB_whenUseArrayCopyPosition_thenArrayCopiedFromAToBInResult() {
+        int[] a = {34, 22, 44, 2, 55, 3};
+        int[] b = new int[a.length];
+
+        // copy 2 elements from a, starting at a[1] to b, starting at b[3]
+        System.arraycopy(a, 1, b, 3, 2);
+        Assert.assertArrayEquals(new int[] {0, 0, 0, 22, 44, 0}, b);
+    }
+}

core-java/src/test/java/com/baeldung/system/SystemNanoTest.java

@@ -0,0 +1,16 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SystemNanoTest {
+
+    @Test
+    public void givenSystem_whenCalledNanoTime_thenGivesTimeinResult() {
+        long startTime = System.nanoTime();
+        // do something that takes time
+        long endTime = System.nanoTime();
+
+        Assert.assertTrue(endTime - startTime < 10000);
+    }
+}

core-java/src/test/java/com/baeldung/system/SystemPropertiesTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Properties;
+
+public class SystemPropertiesTest {
+
+    @Test
+    public void givenSystem_whenCalledGetProperty_thenReturnPropertyinResult() {
+        Assert.assertNotNull(System.getProperty("java.vm.vendor"));
+    }
+
+    @Test
+    public void givenSystem_whenCalledSetProperty_thenSetPropertyasResult() {
+
+        // set a particular property
+        System.setProperty("abckey", "abcvaluefoo");
+        Assert.assertEquals("abcvaluefoo", System.getProperty("abckey"));
+    }
+
+    @Test
+    public void givenSystem_whenCalledClearProperty_thenDeletePropertyasResult() {
+
+        // Delete a property
+        System.clearProperty("abckey");
+        Assert.assertNull(System.getProperty("abckey"));
+    }
+
+    @Test
+    public void givenSystem_whenCalledGetPropertyDefaultValue_thenReturnPropertyinResult() {
+
+        System.clearProperty("dbHost");
+        String myKey = System.getProperty("dbHost", "db.host.com");
+        Assert.assertEquals("db.host.com", myKey);
+    }
+
+    @Test
+    public void givenSystem_whenCalledGetProperties_thenReturnPropertiesinResult() {
+        Properties properties = System.getProperties();
+
+        Assert.assertNotNull(properties);
+    }
+
+    @Test
+    public void givenSystem_whenCalledClearProperties_thenDeleteAllPropertiesasResult() {
+
+        // Clears all system properties. Use with care!
+        System.getProperties().clear();
+
+        Assert.assertTrue(System.getProperties().isEmpty());
+    }
+}