测试代码

public class Test {
    private static int x[]=new int[1];  
    private static int xx[];  
    static int j;
    public static void main(String[] args) {    
        int i;
        System.out.println(x[0]);    //输出0
        System.out.println(j);       //输出0
//       System.out.println(xx[0]);   //空指针异常
//        System.out.println(i);       //局部变量i不能加任何访问修饰符，要输出的时候必须赋值
    }
}

class Test1 {    
  
    public static void main(String[] args) {  
        byte x=127;
        double y=12.3;
        System.out.println(x/y);//最终结果是一个double型
        System.out.println(x%y);//最终结果是一个double型0
    }
}

public class A {
    public int i=0;
   A()
   {}
    public A(String a)
    {
        i=1;
    }//定义了有参数的构造方法通常还需要定义一个无参的构造方法
}

public class A {
    public int i=0;
   A()
   {}
    public A(String a)
    {
        i=1;
    }//定义了有参数的构造方法通常还需要定义一个无参的构造方法
}
 
 
public class Test3 {
    public static void main(String[] args) {       
        final StringBuffer s1=new StringBuffer();
        final StringBuffer s2=new StringBuffer();       
        new Thread()
        {
            public void run()
           {
               synchronized (s1)
               {
                   s1.append("A");
                   synchronized (s2)
                   {
                       s2.append("B");
                       System.out.print(s1);
                       System.out.print(s2);
                   }
               }
           }
        }.start();
       
        new Thread(){
            public void run()
            {
                synchronized(s2)
                {
                    s2.append("C");
                    synchronized(s1)
                    {
                        s1.append("D");
                        System.out.print(s2);
                        System.out.print(s1);
                    }
                }
           }
        }.start();
    }
}   //ABBCAD
 
    public static void main(String[] args) {
        class Foo{
            public int i=3;
        }
        Object o=(Object)new Foo();
        Foo foo=(Foo)o;   
        System.out.println(foo.i);      //3       
    }  
 
   public static void main(String[] args) {
        boolean flag;
        int i=0;
        do{
            flag=false;
            System.out.print(i++);;
            flag=i<10;
            continue;      
        }while((flag)?true:false);   //注意这里的分号不要掉
    }   //0123456789