Added Builder Design pattern implementation in Java and its test

src/main/java/com/designpatterns/builderpattern/Desktop.java

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+package src.main.java.com.designpatterns.builderpattern;
+
+/**
+ * The Builder is a design pattern designed to provide a flexible solution to various object creation problems in
+ * object-oriented programming. The intent of the Builder design pattern is to separate the construction of a complex
+ * object from its representation.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Builder_pattern">Builder Pattern</a>
+ */
+
+public class Desktop {
+    private String CPU;
+    private String RAM;
+
+    private boolean isGraphicCardEnabled;
+    private String operatingSystem;
+    private int diskSizeGB;
+    private String graphicCard;
+
+    private Desktop(DesktopBuilder builder) {
+        this.CPU = builder.CPU;
+        this.RAM = builder.RAM;
+        this.isGraphicCardEnabled = builder.isGraphicCardEnabled;
+        this.operatingSystem = builder.operatingSystem;
+        this.diskSizeGB = builder.diskSizeGB;
+        this.graphicCard = builder.graphicCard;
+    }
+
+    /**
+     * Builder class for the above Desktop class. Constructs the Desktop by invoking the Desktop class constructor and
+     * allows access to set optional fields in the Desktop class.
+     */
+    public static class DesktopBuilder {
+        private String CPU;
+        private String RAM;
+        private boolean isGraphicCardEnabled;
+        private String operatingSystem;
+        private int diskSizeGB;
+        private String graphicCard;
+
+        public DesktopBuilder(String CPU, String RAM) {
+            this.CPU = CPU;
+            this.RAM = RAM;
+        }
+
+        public DesktopBuilder setGraphicCardEnabled(boolean graphicCardEnabled) {
+            this.isGraphicCardEnabled = graphicCardEnabled;
+            return this;
+        }
+
+        public DesktopBuilder setOperatingSystem(String operatingSystem) {
+            this.operatingSystem = operatingSystem;
+            return this;
+        }
+
+        public DesktopBuilder setDiskSizeGB(int diskSize) {
+            this.diskSizeGB = diskSize;
+            return this;
+        }
+
+        public DesktopBuilder setGraphicCard(String graphicCard) {
+            this.graphicCard = graphicCard;
+            return this;
+        }
+
+        public Desktop build() {
+            return new Desktop(this);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "Desktop{" +
+                "CPU='" + CPU + '\'' +
+                ", RAM='" + RAM + '\'' +
+                ", isGraphicCardEnabled=" + isGraphicCardEnabled +
+                ", operatingSystem='" + operatingSystem + '\'' +
+                ", diskSizeGB=" + diskSizeGB +
+                ", graphicCard='" + graphicCard + '\'' +
+                '}';
+    }
+}

src/test/java/com/designpatterns/builderpattern/DesktopBuilderTest.java

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+package src.test.java.com.designpatterns.builderpattern;
+
+import org.junit.Assert;
+import org.junit.Test;
+import src.main.java.com.designpatterns.builderpattern.Desktop;
+
+public class DesktopBuilderTest {
+    private final String configOne = "Desktop{CPU='Intel i7', RAM='Corsair Vengeance 3000', isGraphicCardEnabled=true" +
+            ", operatingSystem='Windows 10', diskSizeGB=16, graphicCard='NVIDIA GTX 1080'}";
+    private final String configTwo = "Desktop{CPU='Intel i5', RAM='HyperX Fury v5', isGraphicCardEnabled=true, " +
+            "operatingSystem='Red Hat Enterprise', diskSizeGB=16, graphicCard='NVIDIA RTX 2080'}";
+
+    @Test
+    public void testDesktopBuilder() {
+        Desktop d1 = new Desktop.DesktopBuilder("Intel i7", "Corsair Vengeance 3000")
+                .setDiskSizeGB(16)
+                .setGraphicCard("NVIDIA GTX 1080")
+                .setGraphicCardEnabled(true)
+                .setOperatingSystem("Windows 10")
+                .build();
+        Assert.assertEquals(d1.toString(), configOne);
+
+        Desktop d2 = new Desktop.DesktopBuilder("Intel i5", "HyperX Fury v5")
+                .setDiskSizeGB(16)
+                .setGraphicCard("NVIDIA RTX 2080")
+                .setGraphicCardEnabled(true)
+                .setOperatingSystem("Red Hat Enterprise")
+                .build();
+        Assert.assertEquals(d2.toString(), configTwo);
+    }
+
+}