Java自定义类（简单举例）

package 电话卡;

public class UsePhoneCard {
	public static void main(String arge[]) {
		PhoneCard myCard = new PhoneCard(12345678,1234,50.0,"300");
		System.out.println(myCard.toString());
		
	}
}
 class PhoneCard{
	 long cardNumber;
	 private int password;
	 double balance;
	 String connectNumber;
	 boolean connected;
	 
	 PhoneCard(long cn,int pw,double b,String s){
		 cardNumber = cn;
		 password = pw;
		 if(b>0)
			 balance = b;
		 else
			 System.exit(1);
		 connectNumber = s;
		 connected = false;
	 }
	 boolean performConnection(long cn,int pw) {
		 if(cn == cardNumber && pw == password) {
			 connected = true;
			 return true;
		 }
		 else {
			 connected = false;
			 return false;
		 } 
	 }
	 double getBalance() {
		 if(connected)
			 return balance;
		 else
			 return -1;
	 }
	 void performDail() {
		 if(connected)
			 balance = 0.5;
	 }
	 public String toString() {
		 String s = "电话卡接入号码："+connectNumber
				 +"\n电话卡卡号："+cardNumber
				 +"\n电话卡密码"+password
				 +"\n剩余金额"+balance;
		 if(connected)
			 return (s+"\n电话已接通");
		 else
			 return (s+"\n电话未接通");
	 }
 }