几道简单的面试题求解 （最好说说理由 谢谢）
1Does Java use ASCII characters or Unicode characters?
2What is an 'abstract' class? Choose only one option.
A A class with no methods.
B A class with no concrete subclasses.
C A class with at least one undefined message.
D None of above.
3Explain call by value and call by reference. Which of these two does Java support? Which of these two does C++ support?
4下列代码输出结果是多少 为什么)
import java.util.*;public class Test {
private String value = null; public Test(String v) {
value = v;
} public boolean equals(Test o) {
if (o == this)
return true;
if (o instanceof Test) {
Test test = (Test) o;
return value.equals(test.value);
}
return false;
} public static void main(String[] args) {
List list = new ArrayList();
Test test1 = new Test("object");
Test test2 = new Test("object");
Test test3 = new Test("object");
Object test4 = new Test("object");
list.add(test1); System.out.println(list.contains(test2));
System.out.println(test2.equals(test3));
System.out.println(test3.equals(test4));
}
}5Which of the following is NOT true regarding to RuntimeException?
A RuntimeException is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtul Machine.
B A method is not required to declare in its throws clause any subclasses of RuntimeException that might be thrown during the execution of the method but not caught.
C An RuntimeException is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch.
D NullPointerException is one kind of RuntimeException.
1Does Java use ASCII characters or Unicode characters?
2What is an 'abstract' class? Choose only one option.
A A class with no methods.
B A class with no concrete subclasses.
C A class with at least one undefined message.
D None of above.
3Explain call by value and call by reference. Which of these two does Java support? Which of these two does C++ support?
4下列代码输出结果是多少 为什么)
import java.util.*;public class Test {
private String value = null; public Test(String v) {
value = v;
} public boolean equals(Test o) {
if (o == this)
return true;
if (o instanceof Test) {
Test test = (Test) o;
return value.equals(test.value);
}
return false;
} public static void main(String[] args) {
List list = new ArrayList();
Test test1 = new Test("object");
Test test2 = new Test("object");
Test test3 = new Test("object");
Object test4 = new Test("object");
list.add(test1); System.out.println(list.contains(test2));
System.out.println(test2.equals(test3));
System.out.println(test3.equals(test4));
}
}5Which of the following is NOT true regarding to RuntimeException?
A RuntimeException is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtul Machine.
B A method is not required to declare in its throws clause any subclasses of RuntimeException that might be thrown during the execution of the method but not caught.
C An RuntimeException is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch.
D NullPointerException is one kind of RuntimeException.
2.D
4.false
true
false
5.C
2c？message是methord的笔误？
3java只支持传值，c++都支持
没有笔误就是methods.
to 1楼：
能解释一下答案么？
2.C
3.传值调用，实参和形参在内存中是指向2个不同地址的变量或者说是对象;而传址调用是相同的。JAVA只支持传值调用。C++两种都支持！
4. 输出结果如下：
false //因为test2并未添加到list集合对象中，所以不包含
true //进入到Test类重写的equals方法，必然走向instanceof条件判断
false //Object和Test并不是同一种类型
5.D
A A class with no methods.
B A class with no concrete subclasses.
C A class with at least one undefined message.
D None of above.
=============================================
2.什么是抽象类？(单选)
A.一个类没有方法
B.一个类没有具体的子类
C.一个类至少有一个未定义的消息(或方法)
D.以上都不是故选D特此声明：之前我选择的C是错误的。除非C是“一个类至少有一个未定义的抽象方法”的话才是正确的。
我试了一下：一个抽象类即便一个抽象方法没有也是对的：这样也是可以的
abstract class ppp
{
}
object，而题目的是Test，所以并没有调用该类的的equals()方法而是object的方法。所以是false
(o==null ? e==null : o.equals(e))这个是contains方法执行的代码。
第二个输出True，很明显的按照题目的equals的执行顺序，结果是true
第三个是假，依然是调用Object的Equals方法。
A A class with no methods.
B A class with no concrete subclasses.
C A class with at least one undefined methods.
D None of above.
即使所有的方法都实现了，只要在类前边加上abstract她依然是抽象类
——————————————————————————————————————呃，好吧，这个说的有道理，我试了一下。看来，某种程度上，abstract就是为了阻止实例化了
看清楚，这个不是override的方法，是自定义的一个方法而已
在这list放入的是test1 也就是"object"的内存地址
而不是"object"本身 所以这样肯定是输出 false