幾個(gè)面試題

2019-11-10 22:53:04

字體：大中小

供稿：網(wǎng)友

第1題

package com.demo;import java.util.ArrayList;import java.util.Collection;import java.util.Collections;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Set;/* 數(shù)組String[] strs中有很多重復(fù)的元素，找出出現(xiàn)最多的元素，并返回出現(xiàn)的次數(shù)，(30分) */public class Test1 { public static void main(String[] args) { String[] strs={"張無忌","趙敏","aaa","小昭","張無忌","趙敏","aaa","張無忌"}; Map<String,Integer> map = new HashMap<>(); for (String data : strs) { //檢查map中是否包括data if(map.containsKey(data)){ //把對應(yīng)的value加1 Integer count = map.get(data); count++; map.put(data, count); }else{ //不包括 map.put(data, 1); } } System.out.PRintln(map); Collection<Integer> values = map.values(); List<Integer> list = new ArrayList<>(values); Collections.sort(list); int count = list.get(list.size()-1); Set<Entry<String, Integer>> entrySet = map.entrySet(); for (Entry<String, Integer> entry : entrySet) { if(entry.getValue() == count){ System.out.println(entry.getKey()+"-->"+entry.getValue()); break; } } }}

第2題

package com.demo;import java.sql.Connection;/* 有n個(gè)SQL任務(wù)List<SQL> task需要執(zhí)行update，寫一個(gè)方法要求最多100條SQL執(zhí)行一次事務(wù)提交commit,直到執(zhí)行完畢，不漏任務(wù) 用到的知識(shí)點(diǎn) 批量的概念 */import java.sql.PreparedStatement;public class Test2 { public static void main(String[] args) { test2(); } //用jdbc的批量方法 private static void test2() { long start =System.currentTimeMillis(); //向表中添加1000條數(shù)據(jù) String sql="insert into dept(dname,loc) values(?,?)"; Connection conn =DaoFactory.getConnection(); PreparedStatement stmt = null; try { conn.setAutoCommit(false); stmt = conn.prepareStatement(sql); for(int i=1; i<=1000; i++){ stmt.setString(1, "a"+i); stmt.setString(2, "b"+i); stmt.addBatch(); //添加的緩存 if( i % 100 == 0 ){ stmt.executeBatch();//執(zhí)行批量的語句 stmt.clearBatch();//清空緩存 } } conn.commit(); } catch (Exception e) { e.printStackTrace(); }finally{ DaoFactory.closeAll(null, stmt, conn); } long end =System.currentTimeMillis(); System.out.println( end-start ); //1503毫秒 } private static void test1() { long start =System.currentTimeMillis(); //向表中添加1000條數(shù)據(jù) String sql="insert into dept(dname,loc) values(?,?)"; Connection conn =DaoFactory.getConnection(); PreparedStatement stmt = null; try { stmt = conn.prepareStatement(sql); for(int i=0; i<1000; i++){ stmt.setString(1, "a"+i); stmt.setString(2, "b"+i); stmt.executeUpdate(); } } catch (Exception e) { e.printStackTrace(); }finally{ DaoFactory.closeAll(null, stmt, conn); } long end =System.currentTimeMillis(); System.out.println( end-start ); //21503毫秒 }}

第3題

package com.demo;import java.util.ArrayList;import java.util.List;/* 1.寫一個(gè)方法,將1000元現(xiàn)金隨機(jī)發(fā)給20個(gè)客戶，每個(gè)客戶的金額在30~100之間(30分) */public class Test3 { public static void main(String[] args) { boolean flag = true; while (flag) { int sum = 0; List<Integer> list = new ArrayList<Integer>(); for (int i = 1; i <= 20; i++) { // 產(chǎn)生的隨機(jī)數(shù) int num = (int) (Math.random() * 70 + 30); // 0---1 0.999999 sum += num;// 總金額 list.add(num); if (sum == 1000 && i == 20) { System.out.println(list); flag = false; } } } }}//如果是小額帶兩位小數(shù)的話可以對隨機(jī)數(shù)格式化保留兩位小數(shù)package com.demo;import java.text.DecimalFormat;import java.text.NumberFormat;public class Test4 { public static void main(String[] args) { double num = Math.random(); System.out.println(num); System.out.println(String.format("%.2f", num)); System.out.format("%.2f/n", num); DecimalFormat format = new DecimalFormat("0.00"); String strNum = format.format(num); System.out.println(strNum); }}

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