class ValHold{
public int i = 10;
}
public class ObParm{
public void amethod(){
ValHold v = new ValHold();
another(v);
System.out.println(v.i);
}
public void another(ValHold v){
v.i = 20;
ValHold vh = new ValHold();
v =vh;
System.out.println(v.i);
}
public static void main(String[] argv){
ObParm o = new ObParm();
o.amethod();
}
}
程序运行结果为什么,如果编译错误,指出错误原因
答案: 10 20.2)
class A {
public staticvoid a() {
System.out.println("super!");
}
public String toString() {
return “a!”;
}
}
class TestStatic extends A {
public static void a() {
System.out.println("child!");
}
public static void main( String[] args) {
A obj = new TestStatic();
System.out.println(obj);
obj.a();
}
}
输出结果,如果编译错误指出错误原因.
答案:
有static，输出
a!
super!
3)
public class Inc{
public static void main(String argv[]){
Inc inc = new Inc();
int i =0;
inc.fermin(i);
i = i++;
System.out.println(i);
}
void fermin(int i){
i++;
}
}
输出结果,如果编译错误指出错误原因
答案:
0;
4)
public class Agg{
static public int i=10;
public static void main(String argv[]){
switch(i){
case 1:
System.out.println("one");
default:
System.out.println("default");
case 10:
System.out.println("ten");
}
}
}
输出结果:
答案:
default, ten.
5)
boolean flag = false;
if (flag = true) {
System.out.println("true");
}else{ System.out.println("false");}
输出结果,如果编译错误,指出错误所在..
答案:
True
6)
public class Test {
public static void test() {
this.print();
}
public static void print() {
System.out.println("Test");
}
public static void main(String args []) {
test();
}
}
输出结果,如果编译错误,指出错误所在.
答案
编译错误,静态方法不可使用this
7)
1.StringBuffer sb = new StringBuffer("abc");
2.String s = new String("abc");
3.sb.append("def");
4.s.append("def");
5.sb.insert(1, "zzz");
6.s.concat(sb);
7.s.trim();
指出哪些非法,说明理由
答案
4和6非法
理由:String属于包裹类,也称为不可变类
8)数组的初始化下面哪些是错误的
1 int a[] = {1,2,3};
2 int []b[] = {{1,2,3},{1,2,3}};
3 int d[2] = {1,2,3};
4 int d[] = {1,2,3};
5 int []e = {0,0,0};
6 char c[] = {'a', 'b'};
错误为,并说明理由
答案:
3
9)
public class Test8 {
public static void main(String [] args){
Base b = new Subclass();
System.out.println(b.x);
System.out.println(b.method());
}
}
class Base{
int x = 2;
int method(){
return x;
}
}
class Subclass extends Base{
int x = 3;
int method(){
return x;
}
}
指出运行结果:
2
3
10)
abstract class MineBase {
abstract void amethod();
static int i;
}
public class Mine extends MineBase{
public static void main(String argv[]){
int[] ar = new int[5];
for(i = 0;i < ar.length;i++)
System.out.println(ar[i]);
}
}
指出运行结果,如果编译错误指出错误原因
答案:
编译错误,抽象类必须重写
11)
class Base {
//void speak() {
// System.out.println("Base");
// }
}
class Sub extends Base {
void speak() {
System.out.println("Sub");
}
}
public class Test9{
public static void main(String argv[]){
Base b = new Sub();
b.speak();
}
}
指出运行结果,如果编译错误指出错误原因
编译错误,父类没有类似方法.
11)
public class Arg{
String[] MyArg;
public static void main(String argv[]){
MyArg=argv;
}
public void amethod(){
System.out.println(argv[1]);
}
}
指出运行结果,如果编译错误指出错误原因
编译错误,静态方法不可以调用动态属性
12)
public class Test{
public static void main(String[] args) {
amethod();
}
static void amethod(){
try{
System.out.println("abcd");
return;
}finally {
System.out.println("123456");
}
}
}
指出运行结果,如果编译错误指出错误原因
答案:
abcd
123456
13)
class XXX {
public static void main(String[] args) {
String s1 = "abcde";
String s2 = "abcde";
s1.toUpperCase();
if (s1 == s2)
System.out.println("YES");
else
System.out.println("NO");
}
}
指出输出结果,如果编译错误指出错误原因.
答案:
YES
14)
1. public class Papa {
2. int i;
3. Papa(int j) { i = j; }
4. }
5.
6. class Child extends Papa {
7. Child() { i = 5; }8. public static void main(String[] args) {
9. new Child();
10. }
11. }
指出输出结果,如果编译错误指出错误原因和所在行
答案:
编译错误,父类构造函数没有初始化
15)
public class T{
public static void main(String[] arg){
StringBuffer a = new StringBuffer ("A");
StringBuffer b = new StringBuffer ("B");
operate (a,b);
System.out.println(a + "," +b);
}
static void operate (StringBuffer x, StringBuffer y) {
x.append (y);
y = x;
}
}
指出输出结果,如果编译错误指出错误原因
输出
AB,B
16)
1. String s1 = "abc";
2. String s2 = s1;
3. String s3 = "abc";
在三个声明中将有几个对象产生
答案:1
16)
public class StrEq{
public static void main(String argv[]){
StrEq s = new StrEq();
}
private StrEq(){
String s = "Marcus";
String s2 = new String("Marcus");
if(s == s2){
System.out.println("we have a match");
}else{
System.out.println("Not equal");
}
}
}
指出输出结果,如果编译错误指出错误原因.
答案:
Not equal
