java笔试题

 1.
public class TT {


public static void main(String[] args)  {
String a = "A";
StringBuffer b = new StringBuffer("B");
StringBuffer c = new StringBuffer("C");
change(a,b,c);
System.out.println(a+","+b+","+c);
}
static void change(String s,StringBuffer s1,StringBuffer s2){
s= s+"1";
s1.append("1");
s2 = new StringBuffer("c1");
}
A:  A,B1,C
B:  A1,B1,C1
C:  A,B,C

2.
class Tree{
void say(){}
}
class Point extends Tree{
void say(){
System.out.println("point");
}
}
class What extends Tree{
void say(){
System.out.println("what");
}
}
class Test{
static void aa(Tree t){
t.say();
}
public static void main(String[] args) {
Tree point = new Point();
Tree what = new What();
aa(point);
aa(what);
}
}
A:point
B:what
C:什么都不输出
D:编译不能通过

3：写出该程序运行后控制台的输出
public class TestString{
public static void callA(int a,StringBuffer sb){
a = 10;
sb.append(" luck");
print(a,sb);
}
public static void callB(int a,StringBuffer sb){
a = 33;
sb = new StringBuffer("haha");
print(a,sb);
}
public static void print(int a,StringBuffer sb){
System.out.println(a);
System.out.println(sb.toString());
}
public static void main(String[] args) {
int a = 100;
StringBuffer sb = new StringBuffer("GOOD");
TestString.callA(a,sb);
TestString.callB(a,sb);
print(a,sb);
}

}
4：写出该程序运行后控制台的输出
class Parent{
Parent(){
System.out.println("Parent构造方法");
}
static{
System.out.println("Parent static");
}
}
class Child extends Parent{
Child(){
System.out.println("Child构造方法");
}
static{
System.out.println("Child static");
}
}
public class TestCons {
public static void main(String[] args) {
Parent chi = new Child();
}
}