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。