1.Java創建自定義類數組方法::
Student [] stu =新生[3]; for(int i = 0; i <3; i ++){stu [i] = new student();}2.否則會提示空指針異常
包裝項目;導入java.io。 *;導入java.util.scanner; class Student {private int ID;私有字符串名稱;私人int得分; public void setID(int id){this.id = id; } public int getId(){返回this.id; } public void setName(string name){this.name = name; } public String getName(){return this.name; } public void setScore(int score){this.score = score; } public int getCore(){返回this.score; }} public類Project2 {文件file = new file(“ e:/data.txt”); filewriter filewrite = null; BufferedWriter寫入= null; fileReader fileRead = null; bufferedReader read = null;學生[] stu =新生[3]; public void put(){try {filewrite = new filewriter(file); } catch(ioexception e){// todo catch塊e.printstacktrace(); } write = new BufferedWriter(filewrite); for(int i = 0; i <3; i ++){system.out.println(“請輸入第” +(i + 1) +”個學生的ID,姓名,成績:”);掃描儀IN =新掃描儀(System.in);嘗試{字符串str = in.nextline();字符串數據[] = str.split(“”); for(int j = 0; j <3; j ++){write.write(data [j]); write.newline(); }} catch(ioexception e){// todo catch塊e.printstacktrace(); }}嘗試{write.close(); filewrite.close(); } catch(ioexception e){// todo catch塊e.printstacktrace(); }} public void get(){int sum = 0;雙ave;嘗試{fileread = new FileReader(file); } catch(filenotfoundException e){// todo catch塊e.printstacktrace(); } read = new BufferedReader(fileread); for(int i = 0; i <3; i ++){stu [i] = new student();嘗試{stu [i] .setId(integer.parseint(read.readline())); stu [i] .setName(read.Readline()); stu [i] .setscore(integer.parseint(read.readline())); } catch(異常e){// todo catch塊e.printstacktrace(); }} for(int i = 0; i <3; i ++){sum += stu [i] .getScore(); } ave = sum * 1.0/3; system.out.println(“學生的平均成績為:” + ave);嘗試{read.close(); fileread.close(); } catch(ioexception e){// todo catch塊e.printstacktrace(); }} public static void main(string [] args){project2 pro = new Project2(); pro.put(); pro.get(); }}}總結:
這樣我們就可以在項目當中,根據項目需求自己來定義想要的數組。