15道非常经典的Java面试题 附详细答案

/*** 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) 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: "+10000000+", actual be: "+count);System.out.println("4. volatile不能保证线程安全");}private static void five(){ArrayList 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");}