适合大一复习期末考试的→java

2019-06-11 05:57:00 392 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

别再手动写JSON了！用Node-RED OPC UA节点5分钟搞定楼宇温湿度数据采集本文介绍了如何利用Node-RED和OPC UA节点快速实现楼宇温湿度数据的自动化采集与JSON格式转换。通过可视化工具Node-RED，开发者无需编写复杂代码，5分钟内即可完成从传感器到数据输出的全流程配置，大幅提升智慧楼宇和工业物联网项目的实施效率。阅读详情

更简单的写法 1.List接口 import java.util.*; public class Example｛ Public static void main(String[] args){ List list = new ArrayList(); List.add(“a”); List.add(“b”); List.add(“c”); Object obj = list.get(0); String s = (String)obj; System.out.prrintln(s); Itearator it = list.iterator(); While(it.hasNext()){ Object obj = it.next(); System.out.println(); } } } 2.Hashmap集合 import java.util.*; Public class Example{ Public static void main(String[] args){ Map map = new HashMap(); map.put (“Tom”,”Tom的衣服”)； map.put (“Jim”,”Jim的鞋子”)； Object obj = map.get(“Jim”); System.out.prrintln(obj); } } 3.Set接口 import java.util.*; Public class Example{ Public static void main(String[] args){ Set<string> set = new HashSet<string>(); Set.add(“abc”); Set.add(“efg”); Set.add(“abc”); for(String s : set){ System.out.prrintln(s); } } } 4.输入字节流读取文件 import java.io.*; Public class Example{ Public static void main(String[] args) throws Exception { FileInputstream in = new FileInputstream(“test.txt”); int b; While((b = in.read()) != -1){ System.out.prrintln(b); } in.close(); } } 5.输出字节流 import java.io.*; Public class Example{ Public static void main(String[] args) throws Exception { FileOutputstream in = new FileOutputstream(“example.txt”); String str = “传智播客”; Byte[] b = str.getBytes(); for(int i =0;i<b.length;i++){ Out.write(b[i]); } out.close; } } 6.文件的拷贝 import java.io.*; Public class Example{ Public static void main(String[] args) throws Exception { Inputstream in = new FileInputstream(“source\\example.txt”); Outputstream in = new FileInputstream(“target\\example.txt”); int b; while((b = in.read())!= -1){ out.write(b); } in.close(); out.close; } } 7.包装类（基本数据类型和串相互转换） Public class Example{ Public static void main(String[] args) { String s = “1234”; int a = Integer.parseInt(s);//字符串转整数 double d = Double. Integer.parseInt(s);//字符串转小数 String x = String.valueOf(a);//整数转字符 System.out,println(a); } } 8.Random类（0到100之间的随机数） import java.util.Random; Public class Example{ Public static void main(String[] args) { Random r = new Random(); for(int x = 0;x<100;x++){ System.out,println(r.nextInt(100)); } } } 9.Math类（重点） Public class Example{ Public static void main(String[] args) { int a = Math.abs(-32); long b = Math.round(3.14); int x = 4; int y = 6; int max = Math.max(x,y) System.out.println(); } } 10.StringBuffer类 Public class Example{ Public static void main(String[] args) { StringBuffer b = new StringBuffer(“we are”); b.appenf(“ students”); b.Inset(6,“ good”); System.out,println(b); } } 11.字符串的拼接（截取和分割） Public class Example{ Public static void main(String[] args) { String str1 = “abc”; string str2 = “def”; String str3 = str1 +str2 System.out,println(str3); } } 12.字符串的判断操作 Public class Example{ Public static void main(String[] args) { String str1 = “abc”; string str2 = “abc”; booleam t; if(s1==s2) t=true else t=false System.out,println(t); 13.String类的初始化 Public class Example{ Public static void main(String[] args) { String str1 =new String(); String str2 = new String (“abc”); char[] charArray = new char[]{‘O’,’E’’F’}; String str3 = new String(charArray); System.out,println(“a” +str1 +”b”); System.out,println(str2); System.out,println(str3); } } 14.数组求和 Public class Example{ Public static void main(String[] args) { int[] arr = {1,2,3,4,5}; int sum = 0; for(int i = 0; i<arr.length;i++) sum+=(arr[sum]); } System.out,println(arr[sum]); } } 15.一是方法名相同，二是参数个数或参数类型不同 Public class Example{ Public static void main(String[] args) { int sum1 = add(1,2); int sum2 = add(1,2,3); double sum3 = add(1.2,2.3); System.out,println(“sum1” + sum1); System.out,println(“sum2” + sum2); System.out,println(“sum3” + sum3); } Public static int add(int x,int y){ Return x+y; } Public static int add (int x,int y){ Return x+y+2; } Public static double add(double x, double y){ return x+y; } } 16.单词分离 Public class Example{ Public static void main(String[] args) { String s = “we are good students”; String[] arr = S.split(“”); for(int i =0; i<arr.length;i++){ System.out,println(“arr[i]”); } for(String a:arr){ System.out,println(a); } } } 17.判断两字符串是否相等 Public class Example{ Public static void main(String[] args) { String s1 = “abc”; String s2 = mew String(“abc”); String s = s1 +s2; int len = s.length(); s = s.trim(); booleam t; if(s1 == s2) t =ture; else t=false; } } 18.遍历目录下的文件 import java.io.*; Public class Example{ Public static void main(String[] args) throws Exception { File file = new File(“D:\\ ”); if(file.isDirectort()){ String[] names = file.list(); for(int i = 0;i<names.length;i++){ System.out,println(names[i]); } }

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