JAVA 第4章 类与对象 练习1

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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);
}
}

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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());
}
}

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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));
}
}

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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)
}
}
}

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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");
}
}