java面试题目

//如何读大文件：

package com.zhoubo;  

import java.io.RandomAccessFile;  
import java.nio.ByteBuffer;  
import java.nio.channels.FileChannel;  
  
public class ReadBigFile {  
  
    /*
     * @param args 
     */  
    public static void main(String[] args)throws Exception {  
        //定义缓冲区的大小为1KB  
        int bufSize = 1024;  
        byte [] bs = new byte[bufSize];  
          
        ByteBuffer byteBuffer = ByteBuffer.allocate(bufSize);  
        FileChannel channel = new RandomAccessFile("c://dmmsi.log","r").getChannel();  
        int size;  
        //读取到输入流的最后  
        while((size = channel.read(byteBuffer))!=-1){  
            byteBuffer.rewind();  
            byteBuffer.get(bs);  
            System.out.println(new String(bs, 0, size));  
            byteBuffer.clear();           
        }  
        channel.close();  
          
    }  
  

提供一个字符串，转化成10进制输出，例如“AA”,输出170 ：

package com.zhoubo;  
/** 
 *
 * @author BZ70000910 
 * 
 */  
public class ZTETest {  
  
    /** 
     * @param args 
     */  
    public static void main(String[] args) {  
        String str = "ABCDE" ;  
        ZTETest test = new ZTETest();  
        System.out.println(test.decimal(str));  
    }  
  
    public int decimal(String str){  
        char [] chars;  
        if(str != ){  
            chars = str.toCharArray();  
        }else  
            chars = ;  
        int sum = 0;  
        int j = 0;  
        for(int i = str.length()-1; i>=0 ; i--){  
            sum = sum + (getValue(chars[i])<<(4*j));  
            j++;  
        }  
        return sum;  
    }  
      
    public int getValue(char x){  
        switch(x){  
            case '0': return 0;  
            case '1': return 1;  
            case '2': return 2;  
            case '3': return 3;  
            case '4': return 4;  
            case '5': return 5;  
            case '6': return 6;  
            case '7': return 7;  
            case '8': return 8;  
            case '9': return 9;  
            case 'A': return 10;  
            case 'B': return 11;  
            case 'C': return 12;  
            case 'D': return 13;  
            case 'E': return 14;  
            case 'F': return 15;  
            default: return 0 ;  
        }  
    }  
}  

输入“我ABC汉DEF”，6，应该输出为“我ABC”而不是“我ABC+汉的半个”。

package com.zhoubo;  
 
public class ZTETest2 {  
  
    /** 
     * @param args 
     */  
    public static void main(String[] args) {  
        String str = "我abc汉def";  
        ZTETest2 test = new ZTETest2();  
        System.out.println(str.substring(0,4));  
        System.out.println(test.StringCutByByte(str, 2));  
  
    }  
      
    public String StringCutByByte(String str, int index){  
        String temp = ;  
        byte [] bytes = str.getBytes();  
        byte [] bytetemp = new byte[index];  
        for(int i=0; i<index ; i++ ){  
            bytetemp[i] = bytes[i];  
            System.out.println(bytes[i]);  
        }  
        if(index>1){  
            if(bytes[index-1]<0&&bytes[index-2]>0){             
                //第三个参数表示要解码的字节数  
                temp = new String(bytetemp,0,index-1);            
            }else{  
                temp = new String(bytetemp);  
            }         
        }else{  
            if(bytes[index-1]<0){  
                temp = ;  
            }else  
                temp = new String(bytetemp,0,1);  
        }  
          
        return temp;  
    }  
  
}