JAVA 第4章 类与对象 练习1

class Fish{
	int weight=1;
}
class Lake{
	Fish fish;
	void setFish(Fish s){
		fish=s;
	}
	void foodFish(int m){
		fish.weight=fish.weight+m;
	}
}
public class E {
	public static void main(String[] args) {
		Fish redFish=new Fish();
		Lake lake=new Lake();
		System.out.println(redFish.weight);
		lake.setFish(redFish);
		lake.foodFish(120);
		System.out.println(redFish.weight);
		System.out.println(lake.fish.weight);
	}
}

class B{
	int x=100,y=200;
	public void setX(int x){
		x=x;
	}
	public void setY(int y){
		this.y=y;
	}
	public int getXYsum(){
		return x+y;
	}
}
public class E{
	 public static void main(String args[]){
		 B b=new B();
		 b.setX(-100);
		 b.setY(-200);
		 System.out.println("sum="+b.getXYsum());
	 }
}

class B{
	int n;
	static int sum=0;
	void setN(int n){
	this.n=n;	
	}
	int getSum(){
		for(int i=1;i<=n;i++){
			sum=sum+i;
		}
		return sum;
	}
}
public class E {
	public static void main(String[] args) {
		B b1=new B(),b2=new B();
		b1.setN(3);
		b2.setN(5);
		int s1=b1.getSum();
		int s2=b2.getSum();
		System.out.println(s1+s2);
	}
	}

class A{
	double f(int x,double y){
		return x+y;
	}
	int f(int x,int y){
		return x*y;
	}
}
public class E {
	public static void main(String[] args) {
		A a=new A();
		System.out.println(a.f(10, 10));
		System.out.println(a.f(10, 10.0));
	}
}

public class E {
	public static void main(String[] args) {
		f(1,2);
		f(-1,-2,-3,-4);//给参数传值时，实参的个数很灵活
		f(9,7,6);
	}
	public static void f(int ... x){
		//x是可变参数的代表，代表若干个int型参数
		for(int i=0;i<x.length;i++){
			//x.length是x代表的参数个数
			System.out.print(" "+x[i]);
			//x[i]是x代表的第i个参数(类似数组)
		}
	}
}

package E;
class AAA{
	static {//静态块
		System.out.println("我是AAA中的静态块!");
	}
}
public class E {
        static {//静态块
        	System.out.println("我是最先被执行的静态块！");
        }
        public static void main(String args[]) {
        	AAA a=new AAA();//AAA的字节码进入内存
        	System.out.println("我在了解静态(static)块");
        }
}