done

src/main/java/com/github/hcsp/encapsulation/UserBuilder.java

@@ -1,6 +1,42 @@
 package com.github.hcsp.encapsulation;
 
-public class UserBuilder {
+public final class UserBuilder {
     // 请在这里使用builder模式建造User对象
     // 所需的接口请参阅UserBuilderTest测试类
+    private String firstName;
+    private String lastName;
+    private String phoneNumber;
+    private String address;
+
+    public UserBuilder() {
+    }
+
+    public static UserBuilder aUser() {
+        return new UserBuilder();
+    }
+
+    public UserBuilder withFirstName(String firstName) {
+        this.firstName = firstName;
+        return this;
+    }
+
+    public UserBuilder withLastName(String lastName) {
+        this.lastName = lastName;
+        return this;
+    }
+
+    public UserBuilder withPhoneNumber(String phoneNumber) {
+        this.phoneNumber = phoneNumber;
+        return this;
+    }
+
+    public UserBuilder withAddress(String address) {
+        this.address = address;
+        return this;
+    }
+
+    public User build() {
+        return new User(firstName, lastName, phoneNumber, address);
+    }
+
 }

src/test/java/com/github/hcsp/encapsulation/UserBuilderTest.java

@@ -6,13 +6,11 @@
 public class UserBuilderTest {
     @Test
     public void canUseBuilderToCreateObjects() {
-        User user =
-                new UserBuilder()
-                        .firstName("德华")
-                        .lastName("刘")
-                        .phoneNumber("我也不知道")
-                        .address("可能在地球上吧")
-                        .build();
+        User user = new UserBuilder()
+                .withFirstName("德华")
+                .withLastName("刘")
+                .withPhoneNumber("我也不知道")
+                .withAddress("可能在地球上吧").build();
         Assertions.assertEquals("德华", user.getFirstName());
         Assertions.assertEquals("刘", user.getLastName());
         Assertions.assertEquals("我也不知道", user.getPhoneNumber());