物件和類的定義

過載

public class Overloading {
 
	public int test(){
		System.out.println("test1");
		return 1;
	}
 
	public void test(int a){
		System.out.println("test2");
	}	
 
	//以下兩個引數型別順序不同
	public String test(int a,String s){
		System.out.println("test3");
		return "returntest3";
	}	
 
	public String test(String s,int a){
		System.out.println("test4");
		return "returntest4";
	}	
 
	public static void main(String[] args){
		Overloading o = new Overloading();
		System.out.println(o.test());
		o.test(1);
		System.out.println(o.test(1,"test3"));
		System.out.println(o.test("test4",1));
	}
}
 

test1
1
test2
test3
returntest3
test4
returntest4

多型

public class test2 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		a am = new a();
		a an = new a();
		c cm = new c();
		d dm =  new d();
		
//		am.cc(new a(){
//			
//			@Override
//			public void cc(b bm) {
//				// TODO Auto-generated method stub
//				System.out.println("sdjghi");
//				
//			}	
//		});
		
//		am.cc(new b(){
//			
//			public void cc(b bm){
//					
//			}
//
//			@Override
//			public void ee() {
//				// TODO Auto-generated method stub
//				System.out.println("sdjghi");
//			}
//			
//		});
		
		cm.run(new b(){

			@Override
			public void cc(b bm) {
				// TODO Auto-generated method stub
				System.out.println("sdjghi");
			}

			@Override
			public void ee() {
				// TODO Auto-generated method stub
				System.out.println("sdjghi");
			}
			
			
		});
	
		cm.cc(cm);
		

	}

	private static b bm;
	public interface b{
		
		void cc(b bm);
		
		void ee();
	}
	
	
	
	static class a implements b {
		
//			a am = new a();
		@Override
		public void cc(b bm) {
			// TODO Auto-generated method stub
			
		}

		@Override
		public void ee() {
			// TODO Auto-generated method stub
			
		}	
	}
	
	static class c implements b{
		
		
		public void run( b bv ){
			
			bm =bv;
			bm.ee();
			bm.cc(bv);
		}
		public void play(){
			
			System.out.println("鍛鍊");
			
		}

		@Override
		public void cc(b bm) {
			// TODO Auto-generated method stub
			
			((c) bm).play();
		}

		@Override
		public void ee() {
			// TODO Auto-generated method stub
			
		}
	}
	
	static class d {
		
	}
}
 

sdjghi
sdjghi
鍛鍊

public class PolTest {

	public static class Wine {

		public void name1() {

			System.out.println("茅臺");
		}

		public void name2(String name) {

			System.out.println("五糧液");
		}

		public void name2(String name, int a) {

			System.out.println("五糧液");
		}
	}

	public static class jnc extends Wine {

		public void name1() {

			System.out.println("特醇劍蘭春");
		}

		public void name2(String name) {

			System.out.println("尊享劍蘭春");
		}

		public void name2(String name, int a) {

			System.out.println("至尊劍蘭春");
		}
		public void drink() {
			
			System.out.println("劍蘭春好喝");
		}
		
	}
	public static class dq extends Wine {
		
		public void name1() {
			
			System.out.println("da");
		}
		
		public void name2(String name) {
			
			System.out.println("qu");
		}
		
		public void name2(String name, int a) {
			
			System.out.println("sdf");
		}
		public void drink() {
			
			System.out.println("hfg");
		}
		
	}
	
	
	

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		Wine wine = new dq();
		wine.name2("有");
//		Wine wine = new Wine();
//		jnc jn= new jnc();
//		wine.name1();
//		jn.name1();
		
	}

}
 

Java實現多型有三個必要條件：繼承、重寫、向上轉型。

所以基於繼承實現的多型可以總結如下：對於引用子類的父類型別（繼承），在處理該引用時(重寫，向上轉型)，它適用於繼承該父類的所有子類，子類物件的不同，對方法的實現也就不同，執行相同動作產生的行為也就不同。

常量

public class A {

	public static void main(String[] args) {
		
		final int m =1;
		A a = new A();
		A b = new A();
		String c ="abc";
		String d ="abc";
		final int f =1;
		
		System.out.println(a);
		System.out.println("---------"+b);
		System.out.println(a==b);
		System.out.println(a.equals(b));
		System.out.println(c==d);
		System.out.println(c.equals(d));
		System.out.println(m==f);
		
		
		System.out.println(m);
	}
}

[email protected]
[email protected]
false
false
true
true
true
1

匿名類

類是有class關鍵字來修飾有名稱並有“{}”，例如class A{} ，宣告物件 A a = new A(); 匿名類沒有名稱所以稱為匿名類如：

protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);
	findViewById(R.id.Button03).setOnClickListener(new OnClickListener(){
		@Override
		public void onClick(View v) {
			Intent intent = new Intent(mainActivity.this, fristActivity.class);
			intent.putExtra("data", "mainActivity");
			startActivity(intent);			
		}		
	});
}

new OnClickListener(){
		@Override
		public void onClick(View v) {
					
		}		
	});  這個就是匿名類

原本應該是這樣寫的（不是匿名類的寫法）

protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);
	findViewById(R.id.Button03).setOnClickListener(new A());
}

<pre name="code" class="html">class A implements View.OnClickListener{
@Override
		public void onClick(View v) {
		
	Intent intent = new Intent(mainActivity.this, fristActivity.class);
			intent.putExtra("data", "mainActivity");
			startActivity(intent);	
			
		}

}