目錄

• 給類屬性賦值的方式
• 直接在類裡面賦值
• 在程式賦值
• 通過構造器賦值（提倡）
• 過載
• NULL
• == 只用來比較兩個基礎值是否相等

給類屬性賦值的方式

直接在類裡面賦值

public class Student {
	String name = "張君瑞";
	int age = 23;
	String sex = "男";
	String address = "陽泉平定";
	void sayHi() {
		System.out.println("我叫" + name + ",我今年"
 
 + age + "歲了");
	}
}

這樣做，每個物件出來後都長得一模一樣

public class Test {
	public static void main(String[] args) {	//程式的主入口
		Student stu = new Student();
		Student stu2 = new Student();
		Student stu3 = new Student();
	}
}

在程式賦值

public class Student{
	String name;
	int age;
	String sex;
	String address;
 

	void sayHi() {
		System.out.println("我叫" + name + ",我今年" + age + "歲了");
	}
}

這樣做太麻煩

public class Test {
	public static void main(String[] args) {	//程式的主入口
		Student s1 = new Student();
		s1.name = "zjr";
		s1.age = 23;
		s1.sex = "男";
		s1.address = "陽泉平定巨城連莊";
		s1.sayHi();
		
		Student s2 = new
 
 Student();
		s2.name = "cxl";
		s2.age = 23;
		s2.sex = "女";
		s2.address = "臨汾霍州";
		s2.sayHi();
		
		
		Student s3 = new Student();
		s3.name = "ww";
		s3.age = 24;
		s3.sex = "男";
		s3.address = "陽泉平定巨城連莊";
		s3.sayHi();
		
		Student s4 = new Student();
		s4.name = "wsj";
		s4.age = 24;
		s4.sex = "男";
		s4.address = "晉城陽城";
		s4.sayHi();
	}
}

通過構造器賦值（提倡）

public class Student{
	String name;
	int age;
	String sex;
	String address;
	Student(String name,int age,String sex,String address) {	//構造器 this指代當前類物件 
		this.name = name;
		this.age = age;
		this.sex = sex;
		this.address = address;
	}
	void sayHi() {
		System.out.println("我叫" + name + ",我今年" + age + "歲了");
	}
}

這種方式是提倡的，這樣做就很不錯，程式碼量少，還很清晰，不容易出錯

public class Test {
	public static void main(String[] args) {	//程式的主入口
		Student s1 = new Student("張君瑞",23,"男","平定連莊");
		s1.sayHi();
		
		Student s2 = new Student("成小麗",23,"女","臨汾霍州");
		s2.sayHi();

		Student s3 = new Student("王偉",23,"男","平定連莊");
		s3.sayHi();
		
		Student s4 = new Student("王世傑",23,"男","晉城陽城");
		s4.sayHi();
	}
}

過載

解釋： 方法名相同，引數列表不同（個數，型別，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){}
}

構造方法是可以過載的，目的是去創造不同的物件，符合更多要求的物件

public class Aoo {
	Aoo() {}			//無參構造 系統預設提供，如果我們提供了構造方法，系統就不提供了，如果還想要無參的，就得自己寫
	Aoo(String name, int age) {
		this.name = name;
		this.age = age;
	}
	Aoo(String name) {
		this.name = name;
	}
	Aoo(int age) {
		this("張君瑞",age);	 //通過過載呼叫引數多的構造，進行屬性賦值
	}
}
 

NULL

空： 是針對引用的，如果引用為空，表示不能使用物件了，如果使用物件就會報NullPointerException異常。

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();  //報錯  因為aoo已經為空了，不在aoo不再指向任何物件
	}
}

== 只用來比較兩個基礎值是否相等