diff --git a/src/class18/Test.java b/src/class18/Test.java
index bf1000b..ce723ac 100644
--- a/src/class18/Test.java
+++ b/src/class18/Test.java
@@ -8,18 +8,19 @@ public class Test {
         c.m1();
     }
 }
-class A{
+
+class A {
     int a = 10;
 
-    void m1(){
+    void m1() {
         System.out.println(a);
     }
 }
 
-class B extends A{
+class B extends A {
     int b = 30;
 }
 
-class C extends B{
+class C extends B {
     int a = 30;
 }
diff --git a/src/class19/Test.java b/src/class19/Test.java
index f9e6db1..da4fc60 100644
--- a/src/class19/Test.java
+++ b/src/class19/Test.java
@@ -2,12 +2,12 @@ package class19;
 
 public class Test {
     public static void main(String[] args) {
-        Cat c = new Cat();
-        c.cry();
+        Cat c = new Cat(); //创建对象
+        c.cry();//调用cry方法
 
     }
 }
-class Cat extends  Animal{
+class Cat extends Animal{
     @Override //方法重写的校验注解，会校验与被重写方法的形参和返回值类型是否一致，保证方法重写安全
     public void cry() {
         System.out.println("喵喵喵~~~");
@@ -18,5 +18,4 @@ class Animal{
     public void cry(){
         System.out.println("动物会叫~~~");
     }
-
 }
diff --git a/src/class20/People.java b/src/class20/People.java
new file mode 100644
index 0000000..5f02f8d
--- /dev/null
+++ b/src/class20/People.java
@@ -0,0 +1,30 @@
+package class20;
+
+public class People {
+    private String name;
+    private char sex;
+    public People(){
+
+    }
+
+    public People(String name, char sex) {
+        this.name = name;
+        this.sex = sex;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public char getSex() {
+        return sex;
+    }
+
+    public void setSex(char sex) {
+        this.sex = sex;
+    }
+}
diff --git a/src/class20/Student.java b/src/class20/Student.java
new file mode 100644
index 0000000..c03dc8e
--- /dev/null
+++ b/src/class20/Student.java
@@ -0,0 +1,66 @@
+package class20;
+
+public class Student {
+    private String name;
+    private int age;
+    private char sex;
+    private String schoolName;
+
+    public Student() {
+    }
+
+    public Student(String name, char sex, int age) {
+        //this 调用兄弟构造方法
+        //默认值处理
+        this(name,"黑马程序员",sex,age);
+    }
+
+    public Student(String name, String schoolName, char sex, int age) {
+        this.name = name;
+        this.schoolName = schoolName;
+        this.sex = sex;
+        this.age = age;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    public char getSex() {
+        return sex;
+    }
+
+    public void setSex(char sex) {
+        this.sex = sex;
+    }
+
+    public String getSchoolName() {
+        return schoolName;
+    }
+
+    public void setSchoolName(String schoolName) {
+        this.schoolName = schoolName;
+    }
+
+    @Override
+    public String toString() {
+        return "Student{" +
+                "name='" + name + '\'' +
+                ", age=" + age +
+                ", sex=" + sex +
+                ", schoolName='" + schoolName + '\'' +
+                '}';
+    }
+}
diff --git a/src/class20/Teacher.java b/src/class20/Teacher.java
new file mode 100644
index 0000000..b057385
--- /dev/null
+++ b/src/class20/Teacher.java
@@ -0,0 +1,19 @@
+package class20;
+
+public class Teacher extends People{
+    private String skill;
+    public Teacher(){
+    }
+    public Teacher(String name, char sex, int age, String skill) {
+        super(name, sex);
+        this.skill = skill;
+    }
+
+    public String getSkill() {
+        return skill;
+    }
+
+    public void setSkill(String skill) {
+        this.skill = skill;
+    }
+}
diff --git a/src/class20/Test.java b/src/class20/Test.java
new file mode 100644
index 0000000..da36421
--- /dev/null
+++ b/src/class20/Test.java
@@ -0,0 +1,21 @@
+package class20;
+
+public class Test {
+    public static void main(String[] args) {
+        Zi zi = new Zi(10);
+
+    }
+}
+class Zi extends Fu {
+    public Zi(int a) {
+        super(a);//指定调用有参构造器，防止无参构造器报错
+    }
+}
+class Fu{
+    private Fu(){
+        System.out.println("父类无参构造方法执行了");
+    }
+    public Fu(int a){
+        System.out.println("父类有参构造方法执行了");
+    }
+}
diff --git a/src/class20/Test2.java b/src/class20/Test2.java
new file mode 100644
index 0000000..d599ce1
--- /dev/null
+++ b/src/class20/Test2.java
@@ -0,0 +1,14 @@
+package class20;
+
+public class Test2 {
+    public static void main(String[] args) {
+        Teacher t = new Teacher();
+        t.setName("张三");
+        System.out.println(t.getName());
+        Teacher t1 = new Teacher("张三", '男', 18, "java");
+        System.out.println(t1.getName());
+        System.out.println(t1.getSkill());
+        System.out.println(t1.getSex());
+
+    }
+}
diff --git a/src/class20/Test3.java b/src/class20/Test3.java
new file mode 100644
index 0000000..c04cd15
--- /dev/null
+++ b/src/class20/Test3.java
@@ -0,0 +1,8 @@
+package class20;
+
+public class Test3 {
+    public static void main(String[] args) {
+        Student s = new Student("张三","黑马程序员",'男',18);
+        System.out.println(s.toString());
+    }
+}