个人Java面试题收集

Interface Count{

      short counter = 0;

      void countUp();

}

   public class TestCount implements Count{

   public static void main(String[] args){

      TestCount t = new TestCount();

      t.countUp();

}

public void countUp(){

   for (int x = 6; x>counter; x--, ++counter){

      System.out.print(“ ” + counter);

}

}

}


1.         运行下列程序，会产生什么结果？ 
class StaticA

{

       StaticA() 

       {

               System.out.println("StaticA instructor!");

       }

}

 

public class StaticExsample

{

       static int a;

       static String  str = "abc";


       StaticExsample()

       {

               System.out.println(str);

       }


       {

               System.out.println("block initialized");

       }


       static StaticA  sa1 = new StaticA();


       static 

       {

               System.out.println("static block initialized");

               System.out.println(str);

               str += "def";

       }


       static StaticA  sa = new StaticA();

 

       public static void main(String[] args)

       {

               new StaticExsample();

               new StaticExsample();

       }

}


A. 
StaticA instructor!
static block initialized
abc
StaticA instructor!
block initialized
abcdef
block initialized
abcdef
 
 
 
 
2.看看下一列将要输出的结果：
public class Example{

     String str=new String (“good”);

     char[]ch={‘a’,’b’,’c’};

     public static void main(String args[]) {

          Example ex=new example();

          ex.change(ex.str,ex.ch);

          System.out.print(ex.str  + ”  and  ”);

          System.out.print(ex.ch);

}

public void change(String str,char ch[]) {

     str=”test ok”;

     ch[0]=’g’;

}

}

good and gbc
 
 
 
 
 
 
  下列代码哪一行会出错？ 
  public void modify()  {
    int I,j,k;
    I=100;
    while (I>0) {
      j=I*2;
      System.out.println("  The value of j is  "+j);
      k=k+1;
      I--;
    }
  }
 
 
C.line 7  
编辑器会报错，k没有被赋初始值。
 
 
 
 阅读以下代码，选择正确的答案
​   Interface Count{

      short counter = 0;

      void countUp();

}

   public class TestCount implements Count{

   public static void main(String[] args){

      TestCount t = new TestCount();

      t.countUp();

}

public void countUp(){

   for (int x = 6; x>counter; x--, ++counter){

      System.out.print(“ ” + counter);

}

}

}

 
 
E. Compilation fails  
 
 
 
 
 
 
 
看看下面2个程序
 
 public class Test {

 String str = new String("good");
 char [] ch = {'a','b','c'};
 
 public static void main(String[] args) {
  Test t = new Test();
  t.change(t.str, t.ch);
  System.out.print(t.str+"and");
  System.out.print(t.ch);
 }
 
 public void change(String str,char ch[]){
  str = "test ok";
  ch[0] = 'g';
 }
}

输出结果：
 
goodandabc
 
 
public class Test {

 String str = new String("good");
 char [] ch = {'a','b','c'};
 
 public static void main(String[] args) {
  Test t = new Test();
  t.change(t.str, t.ch);
  System.out.print(t.str+"and");
  System.out.print(t.ch);
 }
 
 public void change(String str,char ch[]){
  this.str = "test ok";
  ch[0] = 'g';
 }
}

输出的结果：
 
test okandgbc
 
 
 这两个程序，关键的是在change()中一个有是str ，一个是this.str。
当使用this.str = "test ok"时，改变了Test类实例str变量的引用，所以结果打印出来的结果为"test okandabc";
t.ch没变，是因为数据类型是引用数据类型。
这些属于个人理解，要是不对还请你指出。