版权声明： https://blog.csdn.net/qq_40905403/article/details/83820949
给类属性赋值的方式
直接在类里面赋值
public class Student {
String name = "张君瑞";
int age = 23;
String sex = "男";
String address = "阳泉平定";
void sayHi() {
System.out.println("我叫" + name + ",我今年" + age + "岁了");
}
}
这样做，每个对象出来后都长得一模一样
public class Test {
public static void main(String[] args) { //程序的主入口
Student stu = new Student();
Student stu2 = new Student();
Student stu3 = new Student();
}
}
在程序赋值
public class Student{
String name;
int age;
String sex;
String address;
void sayHi() {
System.out.println("我叫" + name + ",我今年" + age + "岁了");
}
}
这样做太麻烦
public class Test {
public static void main(String[] args) { //程序的主入口
Student s1 = new Student();
s1.name = "zjr";
s1.age = 23;
s1.sex = "男";
s1.address = "阳泉平定巨城连庄";
s1.sayHi();
Student s2 = new Student();
s2.name = "cxl";
s2.age = 23;
s2.sex = "女";
s2.address = "临汾霍州";
s2.sayHi();
Student s3 = new Student();
s3.name = "ww";
s3.age = 24;
s3.sex = "男";
s3.address = "阳泉平定巨城连庄";
s3.sayHi();
Student s4 = new Student();
s4.name = "wsj";
s4.age = 24;
s4.sex = "男";
s4.address = "晋城阳城";
s4.sayHi();
}
}
通过构造器赋值（提倡）
public class Student{
String name;
int age;
String sex;
String address;
Student(String name,int age,String sex,String address) { //构造器 this指代当前类对象
this.name = name;
this.age = age;
this.sex = sex;
this.address = address;
}
void sayHi() {
System.out.println("我叫" + name + ",我今年" + age + "岁了");
}
}
这种方式是提倡的，这样做就很不错，代码量少，还很清晰，不容易出错
public class Test {
public static void main(String[] args) { //程序的主入口
Student s1 = new Student("张君瑞",23,"男","平定连庄");
s1.sayHi();
Student s2 = new Student("成小丽",23,"女","临汾霍州");
s2.sayHi();
Student s3 = new Student("王伟",23,"男","平定连庄");
s3.sayHi();
Student s4 = new Student("王世杰",23,"男","晋城阳城");
s4.sayHi();
}
}
重载
解释： 方法名相同，参数列表不同（个数，类型，位置）
public class Aoo{
void say(){}
void say(String name){}
void say(String name,int age){}
void say(int age, String name){}
void say(int num){}
}
构造方法是可以重载的，目的是去创造不同的对象，符合更多要求的对象
public class Aoo {
Aoo() {} //无参构造 系统默认提供，如果我们提供了构造方法，系统就不提供了，如果还想要无参的，就得自己写
Aoo(String name, int age) {
this.name = name;
this.age = age;
}
Aoo(String name) {
this.name = name;
}
Aoo(int age) {
this("张君瑞",age); //通过重载调用参数多的构造，进行属性赋值
}
}
NULL
空： 是针对引用的，如果引用为空，表示不能使用对象了，如果使用对象就会报NullPointerException异常。
public class Aoo {
String name;
void sayHi(){}
public static void main(String[] args) {
Aoo aoo = new Aoo();
aoo.name = "zjr";
aoo.sayHi();
aoo = null;
aoo.sayHi(); //报错 因为aoo已经为空了，不在aoo不再指向任何对象
}
}