public class student {
	int age;
	String name;
	public student(int age,String name){
		this.age=age;
		this.name=name;
	}
	public static void main(String[] args) {
		//（類）引用類型 引用變量	創(chuàng)建對(duì)象（new出來(lái)的類中的構(gòu)造方法）
		student s= new student(18,"劉永超");
		s=null;
		System.out.println(s);
		System.out.println(s.age);//發(fā)生異常，因?yàn)橐米兞恐赶騨ull
	}
}

public class student2 {
	int age;
	String name;
	public student2(int a,String s){
		age=a;
		name=s;
	}
	
	public static void main(String[] args) {
		student2 s=new student2(17,"liu");
		student2 ss=s;
		s.age=20;
		ss.age=28;
		System.out.println(s.age);
		//s=ss 判斷兩個(gè)引用對(duì)象(引用變量)是否指指向同一對(duì)象
		System.out.println(s==ss);
	}
}

public class overloadDemo {
	public void test(){
		System.out.println("lala");
	}
	
	public void test(int a){
		System.out.println("heihei");
	}

	public void test(String s){
		System.out.println("xixi");
	}

	public void test(int a,String s){
		System.out.println("caocao");
	}

//	public int test(){不是方法的重載，和返回值沒(méi)有關(guān)系
//		return 1;
//	}
	
	//構(gòu)造方法
	public overloadDemo (){
		System.out.println("無(wú)參構(gòu)造");
	}
	
	public overloadDemo(int a){
		System.out.println("有參構(gòu)造");
	}
	
	public static void main(String[] args) {
		overloadDemo load=new overloadDemo();
		load.test(5);
		load.test(8, "liu");
		
	}
}

public class thisDemo {
	int age;
	public void test(){
		System.out.println(this.age);//此處可以省略this關(guān)鍵字
	}
	
	public void test(int age){
		System.out.println("這是帶有int類的test方法重載");
		this.test();//此處也可以省略this，編譯器會(huì)自己默認(rèn)
	}
	
	public thisDemo(){
		//this(20);
		this(19,"liuyongcaho");//調(diào)用當(dāng)前對(duì)象時(shí)int ，string類型的構(gòu)造方法
		this.age=18;
		System.out.println("這是一個(gè)無(wú)參構(gòu)造方法");
	}
	
	public thisDemo(int age){
		this();
		System.out.println(age);
	}
	
	public thisDemo(int age,String name){
		System.out.println(age+"   "+name);
	}
	
	
	public static void main(String[] args) {
		thisDemo pdd=new thisDemo();
		pdd.test(9);
	}
}

/*
 * 父類（超類）
 */
public class Person {
	int age;
	String name;
	String gender;
	
	public Person(int age,String name){
		this.age=age;
		this.name=name;
		System.out.println(this.age+"  "+this.name);
	}
	public void testperson(){
		System.out.println("我是父類");
	}
}

/*
 * 子類（派生類）
 * extends
 */
public class Teacher extends Person{
	String subject;
	public Teacher(){
		//super();這是父類的無(wú)參構(gòu)造方法
		super(19,"劉德華");
		System.out.println(this.age+" "+this.name);
	}
	
	//方法的重寫(xiě)
	public void testperson(){
		System.out.println("這是子類teacher的testperson方法");
	}
	
	public static void main(String[] args) {
		 Person y=new Teacher();//向上造型
		 y.testperson();
	}
}

public static void main(String[] args) {
	 Person y=new Teacher();//向上造型
	 y.testperson();
}

##### 運(yùn)行結(jié)果：

[外鏈圖片轉(zhuǎn)存中...(img-zydw2DJx-1615567706663)]

##### 結(jié)果分析：

子類在創(chuàng)建對(duì)象時(shí)會(huì)執(zhí)行子類的無(wú)參構(gòu)造方法，而子類的構(gòu)造方法中有父類的有參構(gòu)造方法再執(zhí)行子類中的testperson方法。

####