15道非常经典的Java面试题 附详细答案

试题如下：

参考答案：

import java.io.filenotfoundexception;
import java.io.ioexception;
import java.util.arraylist;
import java.util.concurrent.executorservice;
import java.util.concurrent.executors;

/**
 * created by ysc on 7/26/16.
 */
public class interview {
 private static void one(){
 string str1 = "hello";
 string str2 = "he"+new string("llo");
 system.err.println(str1==str2);
 system.out.println("1. false");
 }
 private static void two(){
 int i = integer.max_value;
 system.err.println((i+1)<i);
 system.out.println("2. 存在一个i, 使得(i+1)<i");
 }
 private static void three(){
 system.err.println("gc is not a java thread, it is a native thread");
 thread.getallstacktraces().keyset().foreach(thread -> system.out.println(thread.getname()+"->"+thread.isdaemon()+" "+thread.getpriority()));
 system.out.println("3. gc线程是daemon线程");
 }
 private static volatile int count = 0;
 private static void four(){
 executorservice executorservice = executors.newcachedthreadpool();
 for(int j=0; j<10; j++){
  executorservice.submit(()->{
  for(int i=0; i<1000000; i++){
   count++;
  }
  });
 }
 system.out.println("count should be: "[phone]+", actual be: "+count);
 system.out.println("4. volatile不能保证线程安全");
 }
 private static void five(){
 arraylist<integer> list = new arraylist<>(20);
 list.add(1);
 system.out.println("debug code, not execute grow method");
 system.out.println("5. list grow 0 times");
 }
 private static void six() {
 system.out.println("bufferedreader's constructor only accepts a reader instance");
 system.out.println("6. new bufferedreader(new fileinputstream(\"a.dat\")); is wrong");
 }
 private static void seven() {
 try{
  if(true){
  throw new ioexception();
  }
 }catch (filenotfoundexception e){
  system.out.print("filenotfoundexception!");
 }catch (ioexception e){
  system.out.print("ioexception!");
 }catch (exception e){
  system.out.print("exception!");
 }
 system.out.println("\n7. ioexception!");
 }
 private static void eight() {
 system.out.println("string s;system.out.println(s); error: variable s might not have been initialized\nrecompile with -xlint:unchecked for details.");
 system.out.println("8. 由于string s没有初始化, 代码不能编译通过");
 }
 private static void nine() {
 system.out.println("5"+2);
 system.out.println("9. 52");
 }
 private static void ten() {
 int i = 2;
 int result = 0;
 switch(i){
  case 1:
  result = result + i;
  case 2:
  result = result + i * 2;
  case 3:
  result = result + i * 3;
 }
 system.out.println("result="+result);
 system.out.println("10. 10");
 }
 private static class null{
 public static void hello(){
  system.out.println("hello");
 }
 public static void main(string[] args) {
  ((null)null).hello();
  null _null = (null)null;
  _null.hello();
 }
 }
 private static class stringexample1{
 string str = new string("good");
 char[] ch = {'a', 'b', 'c'};
 public void change(string str, char[] ch){
  str = "test ok";
  ch[0] = 'g';
 }

 public static void main(string[] args) {
  stringexample1 ex = new stringexample1();
  ex.change(ex.str, ex.ch);
  system.out.print(ex.str+" and ");
  system.out.print(ex.ch);
  system.out.println();
 }
 }
 private static class stringexample2{
 public static void change(string str){
  str = "welcome";
 }

 public static void main(string[] args) {
  string str = "1234";
  change(str);
  system.out.println(str);
 }
 }
 private static class forloop{
 static boolean foo(char c){
  system.out.print(c);
  return true;
 }

 public static void main(string[] args) {
  int i=0;
  for(foo('a');foo('b')&&(i<2);foo('c')){
  i++;
  foo('d');
  }
  system.out.println();
 }
 }
 private static class helloa{
 public helloa(){
  system.out.println("helloa");
 }

 { system.out.println("i'm a class"); }

 static {
  system.out.println("static a");
 }
 }
 private static class hellob extends helloa{
 public hellob(){
  system.out.println("hellob");
 }

 { system.out.println("i'm b class"); }

 static {
  system.out.println("static b");
 }

 public static void main(string[] args) {
  system.out.println("main start");
  new hellob();
  new hellob();
  system.out.println("main end");
 }
 }
 public static void main(string[] args) {
 one();
 two();
 three();
 four();
 five();
 six();
 seven();
 eight();
 nine();
 ten();
 null.main(null);
 stringexample1.main(null);
 stringexample2.main(null);
 forloop.main(null);
 hellob.main(null);
 }
}

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