java基础面试题

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   //运算符优先级问题
   private static void youxianji(){
       //表达式 a = i++ 它等价于 a = i ; i = i + 1;
        //表达式 a = ++i 它等价于   i = i + 1; a = i;

       int k = 0;
       int ret = ++k + k++ + ++k + k;
       System.err.println(ret); //8

       k = 0;
       ret = ++k + k++;
       System.err.println(ret);//2
       System.err.println("k="+k);//2

       k = 0;
       ret = ++k + k++ + ++k ;
       System.err.println(ret);//5
       System.err.println("k="+k);//3
   }

   //运算符问题
    private static void yushuanfu(){
       int i1 = 10, i2 = 10;
         System.err.println("i1 + i2 = " + i1 + i2); //1010
         System.err.println("i1 - i2 = " + (i1 - i2)); //0
         System.err.println("i1 * i2 = " + i1 * i2); //100
         System.err.println("i1 / i2 = " + i1 / i2); //1
    }

   public class Test {

    public void myMethod(String str) {
        System.err.println("string");
    }

    public void myMethod(Object obj) {
        System.err.println("object");
    }

    public static void main(String[] args) {
        Test t = new Test();
        t.myMethod(null); //String
    }

    public static void date() {
        Date date = new Date(); //20120211
        System.err.println(date.getMonth() + " " + date.getDate());//1 11
    }

    public static void Mathtest() {
        double val = 11.5;
        System.err.println(Math.round(val)); //12
        System.err.println(Math.floor(val)); //11.0
        System.err.println(Math.ceil(val)); //12.0
    }

    public void method() {
        System.err.println(super.getClass().getName());
        System.err.println(this.getClass().getSuperclass().getName());
    }

    public static void trueisfalse() {
        String str1 = new String("abc");
        String str2 = new String("abc");
        System.err.println(str1.equals(str2)); //true

        StringBuffer sb1 = new StringBuffer("abc");
        StringBuffer sb2 = new StringBuffer("abc");
        System.err.println(sb1.equals(sb2));     //false
    }

    //结果return 1
    public int method1() {
        int x = 1;
        try {
            return x;
        } finally {
            ++x;
        }
    }

    //结果reutrn 2
    public int method2() {
        int x = 1;
        try {
            return x;
        } finally {
            return ++x;
        }
    }
    //结果return false;
    public static boolean method3() {
        try {
           return true;
       } finally {
         return false;
       }
   }

    public static void inttureorfalse() {
        Integer i1 = 127;
        Integer i2 = 127;
        System.err.println(i1 == i2); //true

        i1 = 128;
        i2 = 128;
        System.err.println(i1 == i2);//false
    }

    public static void stringtrueorfalse() {
        String str1 = "a";
        String str2 = "a";
        String str3 = new String("a");

        System.err.println(str1 == str2); //true
        System.err.println(str1 == str3); //false
        str3 = str3.intern();
        System.err.println(str1 == str3); //true
    }

    public static void sub() {
        System.err.println(12 - 11.9 == 0.1); //false
    }

    public static void set() {
        Set<String> set = new HashSet<String>();
        set.add("one");
        set.add("two");
        set.add("three");
        set.add("four");
        set.add("five");
        for (Iterator<String> it = set.iterator(); it.hasNext();) {
            System.err.println(it.next());
        }
//        结果
//        two
//        five
//        one
//        three
//        four

    }

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