Bài 22: Try, catch, finally trong Java

[ngochieu85]

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package beginers[/color][color=#007700];[/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]scanner[/color][color=#007700]; public class [/color][color=#0000bb]trycatch [/color][color=#007700]{    private [/color][color=#0000bb]int a[/color][color=#007700], [/color][color=#0000bb]b[/color][color=#007700];       public [/color][color=#0000bb]void setab[/color][color=#007700](){        [/color][color=#0000bb]scanner in [/color][color=#007700]= new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]);        try {        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"entry the value of variable a: "[/color][color=#007700]);        [/color][color=#0000bb]this[/color][color=#007700].[/color][color=#0000bb]a [/color][color=#007700]= [/color][color=#0000bb]in[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();        } catch([/color][color=#0000bb]exception e[/color][color=#007700]){            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error 1 " [/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);        }               try {        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"entery the value of variable b: "[/color][color=#007700]);        [/color][color=#0000bb]this[/color][color=#007700].[/color][color=#0000bb]b [/color][color=#007700]= [/color][color=#0000bb]in[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();        } catch([/color][color=#0000bb]exception e[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error 2:" [/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);        }    }[/color][color=#ff8000]// method setab.       [/color][color=#007700]public [/color][color=#0000bb]int geta[/color][color=#007700]() {        return [/color][color=#0000bb]a[/color][color=#007700];    }[/color][color=#ff8000]// method geta.       [/color][color=#007700]public [/color][color=#0000bb]int getb[/color][color=#007700](){        return [/color][color=#0000bb]b[/color][color=#007700];    }[/color][color=#ff8000]//method getb.       [/color][color=#007700]public [/color][color=#0000bb]void change[/color][color=#007700](){        try {            if([/color][color=#0000bb]a[/color][color=#007700]==[/color][color=#0000bb]0 [/color][color=#007700]&& [/color][color=#0000bb]b[/color][color=#007700]==[/color][color=#0000bb]0[/color][color=#007700]){                [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"phuong trinh co vo so nghiem! "[/color][color=#007700]);            }else if([/color][color=#0000bb]a[/color][color=#007700]==[/color][color=#0000bb]0 [/color][color=#007700]&& [/color][color=#0000bb]b[/color][color=#007700]!=[/color][color=#0000bb]0[/color][color=#007700]){                [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"phuong trinh vo nghiem! "[/color][color=#007700]);            }else {                [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nghiem pt: " [/color][color=#007700]+ ((float) (-[/color][color=#0000bb]b[/color][color=#007700]/[/color][color=#0000bb]a[/color][color=#007700])) );            }                   } catch([/color][color=#0000bb]exception e[/color][color=#007700]){            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error here! " [/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);        }    }[/color][color=#ff8000]//method change!       [/color][color=#007700]public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string args [/color][color=#007700][]){        [/color][color=#0000bb]trycatch a [/color][color=#007700]= new [/color][color=#0000bb]trycatch[/color][color=#007700]();        [/color][color=#0000bb]a[/color][color=#007700].[/color][color=#0000bb]setab[/color][color=#007700]();        [/color][color=#0000bb]a[/color][color=#007700].[/color][color=#0000bb]change[/color][color=#007700]();    }[/color][color=#ff8000]// method main.[/color][color=#007700]}[/color] 

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[honglinh166]

bài của mình nè: :d
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package com[/color][color=#007700].[/color][color=#0000bb]hanhnv[/color][color=#007700].[/color][color=#0000bb]bai22[/color][color=#007700]; [/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]inputmismatchexception[/color][color=#007700];[/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]scanner[/color][color=#007700]; public class [/color][color=#0000bb]bai22 [/color][color=#007700]{     public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string[/color][color=#007700][] [/color][color=#0000bb]args[/color][color=#007700]) {        [/color][color=#0000bb]mathcal mc [/color][color=#007700]= new [/color][color=#0000bb]mathcal[/color][color=#007700]();        try {            [/color][color=#0000bb]mc[/color][color=#007700].[/color][color=#0000bb]inputdata[/color][color=#007700]();            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"******************"[/color][color=#007700]);            [/color][color=#0000bb]mc[/color][color=#007700].[/color][color=#0000bb]showresult[/color][color=#007700]();        } catch ([/color][color=#0000bb]inputmismatchexception e[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error: please enter number, not string!"[/color][color=#007700]);        } catch ([/color][color=#0000bb]exception e[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error: a mustn\'s equals zero!"[/color][color=#007700]);        }     } } class [/color][color=#0000bb]mathcal [/color][color=#007700]{    private [/color][color=#0000bb]int a[/color][color=#007700], [/color][color=#0000bb]b[/color][color=#007700];     public [/color][color=#0000bb]void inputdata[/color][color=#007700]() {        [/color][color=#0000bb]scanner s [/color][color=#007700]= new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]);         [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"enter a: "[/color][color=#007700]);        [/color][color=#0000bb]a [/color][color=#007700]= [/color][color=#0000bb]s[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"enter b: "[/color][color=#007700]);        [/color][color=#0000bb]b [/color][color=#007700]= [/color][color=#0000bb]s[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();    }     public [/color][color=#0000bb]void showresult[/color][color=#007700]() {        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700](+[/color][color=#0000bb]a [/color][color=#007700]+ [/color][color=#dd0000]"x + " [/color][color=#007700]+ [/color][color=#0000bb]b [/color][color=#007700]+ [/color][color=#dd0000]" = 0"[/color][color=#007700]);        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"=> x = " [/color][color=#007700]+ (-[/color][color=#0000bb]b [/color][color=#007700]/ [/color][color=#0000bb]a[/color][color=#007700]));    } }[/color] 

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[bocau54]

cho em hỏi là sao eclipse của em mỗi lần khai báo import là nó báo lỗi không nhận ạ? ai biết giải thích hộ em với.
ví dụ như: import basic.numbershandling; này thì nó cứ báo lỗi ạ

ảnh ở bên dưới ạ

[khongbiengioic06]

sao bài này k nói rõ và cụ thể hơn 1 tý về throw và throws thế anh tiasangmoi92, 2 cái này em đang còn mơ hồ quá.

[thuankt4]

sao bài này k nói rõ và cụ thể hơn 1 tý về throw và throws thế anh tiasangmoi92, 2 cái này em đang còn mơ hồ quá.

throws là dùng trên khai báo phương thức còn throw là dùng trong thân phương thức. trên khai báo phương thức nếu dùng throws rồi thì ko cần dùng try catch nữa, còn throw dùng trong thân hàm để ném ngoại lệ ra bên ngoài.

[lyvanhung]

cho mình hỏi , mình để kiểu int thì bắt lỗi chia cho 0 dc, còn chuyển a,b sang kiểu float thì lại ko bắt lỗi dc.
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[/color][color=#ff8000]/* * to change this license header, choose license headers in project properties. * to change this template file, choose tools | templates * and open the template in the editor. */[/color][color=#0000bb]package bai22trycatch[/color][color=#007700];    [/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].*;    [/color][color=#ff8000]/** * giải phương trình ax + b = 0 . lập trình hướng đối tượng. các hệ số nhập vào * từ bàn phím. sử dụng try - catch để bẫy các lỗi khi nhập sai kiểu dữ liệu, ví * dụ nhập số lại nhập chữ. bẫy lỗi chia cho 0. * * @author admin */[/color][color=#007700]public class [/color][color=#0000bb]baitap [/color][color=#007700]{    public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string[/color][color=#007700][] [/color][color=#0000bb]args[/color][color=#007700]) {        [/color][color=#0000bb]scanner nhap[/color][color=#007700]=new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]);        [/color][color=#0000bb]int a[/color][color=#007700],[/color][color=#0000bb]b[/color][color=#007700];        try {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nhập a: "[/color][color=#007700]);            [/color][color=#0000bb]a[/color][color=#007700]=[/color][color=#0000bb]nhap[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nhập b: "[/color][color=#007700]);            [/color][color=#0000bb]b[/color][color=#007700]=[/color][color=#0000bb]nhap[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"x = " [/color][color=#007700]+ (-[/color][color=#0000bb]b[/color][color=#007700]/[/color][color=#0000bb]a[/color][color=#007700]));        }catch([/color][color=#0000bb]arithmeticexception e[/color][color=#007700]){            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"lỗi chia cho 0"[/color][color=#007700]);        } catch ([/color][color=#0000bb]inputmismatchexception e[/color][color=#007700]){            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nhập sai kiểu dữ liệu "[/color][color=#007700]);        }  catch ([/color][color=#0000bb]exception e1[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"có lỗi gì đó xảy ra  "[/color][color=#007700]);            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"tên lỗi là: " [/color][color=#007700]+ [/color][color=#0000bb]e1[/color][color=#007700]);        } finally {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"có lỗi hay không thì cái dòng cuối cùng này vẫn được in ra!"[/color][color=#007700]);        }    }}[/color] 

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[hoclaptrinh321]

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package trycatchfinally[/color][color=#007700]; [/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]scanner[/color][color=#007700]; class [/color][color=#0000bb]formula[/color][color=#007700]{static [/color][color=#0000bb]scanner inp[/color][color=#007700];public static [/color][color=#0000bb]void work[/color][color=#007700](){[/color][color=#0000bb]float a[/color][color=#007700]; [/color][color=#0000bb]float b[/color][color=#007700];[/color][color=#0000bb]float x[/color][color=#007700];[/color][color=#0000bb]inp [/color][color=#007700]=new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]); try{[/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"put a= "[/color][color=#007700]);[/color][color=#0000bb]a[/color][color=#007700]=[/color][color=#0000bb]inp[/color][color=#007700].[/color][color=#0000bb]nextfloat[/color][color=#007700]();[/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"put b= "[/color][color=#007700]);[/color][color=#0000bb]b[/color][color=#007700]=[/color][color=#0000bb]inp[/color][color=#007700].[/color][color=#0000bb]nextfloat[/color][color=#007700]();[/color][color=#0000bb]x[/color][color=#007700]=(float)-[/color][color=#0000bb]b[/color][color=#007700]/[/color][color=#0000bb]a[/color][color=#007700];[/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"phuong trinh "[/color][color=#007700]+ [/color][color=#0000bb]a[/color][color=#007700]+[/color][color=#dd0000]"x+"[/color][color=#007700]+[/color][color=#0000bb]b[/color][color=#007700]+[/color][color=#dd0000]"=0 co nghiem la: "[/color][color=#007700]+[/color][color=#0000bb]x[/color][color=#007700]);}catch([/color][color=#0000bb]exception e[/color][color=#007700]){[/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error: "[/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);}}}public class [/color][color=#0000bb]doublefunction [/color][color=#007700]{    public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string [/color][color=#007700][] [/color][color=#0000bb]args[/color][color=#007700]){[/color][color=#0000bb]formula[/color][color=#007700].[/color][color=#0000bb]work[/color][color=#007700]();try{[/color][color=#0000bb]float y[/color][color=#007700];[/color][color=#0000bb]y[/color][color=#007700]=-[/color][color=#0000bb]7[/color][color=#007700]/[/color][color=#0000bb]0[/color][color=#007700];[/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#0000bb]y[/color][color=#007700]);}catch([/color][color=#0000bb]exception a[/color][color=#007700]){[/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error in thread main: "[/color][color=#007700]+[/color][color=#0000bb]a[/color][color=#007700]);} } }[/color] 

[huuduanmobile]

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package baitapvenha[/color][color=#007700];[/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]scanner[/color][color=#007700];[/color][color=#ff8000]/*** làm lại bài giải phương trình ax + b = 0 . lập trình hướng đối tượng. các hệ* số nhập vào từ bàn phím. sử dụng try - catch để bẫy các lỗi khi nhập sai kiểu* dữ liệu, ví dụ nhập số lại nhập chữ. bẫy lỗi chia cho 0.*/[/color][color=#007700]public class [/color][color=#0000bb]buoi22_trycatch [/color][color=#007700]{     public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string[/color][color=#007700][] [/color][color=#0000bb]args[/color][color=#007700]) {          [/color][color=#0000bb]phuongtrinh pt [/color][color=#007700]= new [/color][color=#0000bb]phuongtrinh[/color][color=#007700]();          [/color][color=#0000bb]pt[/color][color=#007700].[/color][color=#0000bb]nhapheso[/color][color=#007700]();          [/color][color=#0000bb]pt[/color][color=#007700].[/color][color=#0000bb]giaipt[/color][color=#007700]();     }} class [/color][color=#0000bb]phuongtrinh [/color][color=#007700]{     private [/color][color=#0000bb]int a[/color][color=#007700], [/color][color=#0000bb]b[/color][color=#007700];     public [/color][color=#0000bb]void nhapheso[/color][color=#007700]() {          [/color][color=#0000bb]scanner sc [/color][color=#007700]= new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]);          [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nhap he so cho phuong trinh:"[/color][color=#007700]);          try {                 [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].print([/color][color=#dd0000]"a = "[/color][color=#007700]);                 [/color][color=#0000bb]seta[/color][color=#007700]( [/color][color=#0000bb]sc[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]());                 [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].print([/color][color=#dd0000]"b = "[/color][color=#007700]);                 [/color][color=#0000bb]setb[/color][color=#007700]([/color][color=#0000bb]sc[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]());           } catch ([/color][color=#0000bb]exception e[/color][color=#007700]) {                  [/color][color=#ff8000]// todo: handle exception                  [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error: "[/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);           }      }      public [/color][color=#0000bb]void giaipt[/color][color=#007700](){          [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"phuong trinh co nghiem: "[/color][color=#007700]);          try {                  [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"x = "[/color][color=#007700]+(float)(-[/color][color=#0000bb]b[/color][color=#007700]/[/color][color=#0000bb]a[/color][color=#007700]));          } catch ([/color][color=#0000bb]exception e[/color][color=#007700]) {                  [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error: "[/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);                 [/color][color=#ff8000]// todo: handle exception          [/color][color=#007700]}     }      public [/color][color=#0000bb]void seta[/color][color=#007700]([/color][color=#0000bb]int a[/color][color=#007700]) {           [/color][color=#0000bb]this[/color][color=#007700].[/color][color=#0000bb]a [/color][color=#007700]= [/color][color=#0000bb]a[/color][color=#007700];     }      public [/color][color=#0000bb]void setb[/color][color=#007700]([/color][color=#0000bb]int b[/color][color=#007700]) {           [/color][color=#0000bb]this[/color][color=#007700].[/color][color=#0000bb]b [/color][color=#007700]= [/color][color=#0000bb]b[/color][color=#007700];     }}[/color] 

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[phongbui]

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package beginers[/color][color=#007700];[/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]scanner[/color][color=#007700]; public class [/color][color=#0000bb]trycatch [/color][color=#007700]{    private [/color][color=#0000bb]int a[/color][color=#007700], [/color][color=#0000bb]b[/color][color=#007700];      public [/color][color=#0000bb]void setab[/color][color=#007700](){        [/color][color=#0000bb]scanner in [/color][color=#007700]= new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]);        try {        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"entry the value of variable a: "[/color][color=#007700]);        [/color][color=#0000bb]this[/color][color=#007700].[/color][color=#0000bb]a [/color][color=#007700]= [/color][color=#0000bb]in[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();        } catch([/color][color=#0000bb]exception e[/color][color=#007700]){            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error 1 " [/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);        }              try {        [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"entery the value of variable b: "[/color][color=#007700]);        [/color][color=#0000bb]this[/color][color=#007700].[/color][color=#0000bb]b [/color][color=#007700]= [/color][color=#0000bb]in[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();        } catch([/color][color=#0000bb]exception e[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error 2:" [/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);        }    }[/color][color=#ff8000]// method setab.      [/color][color=#007700]public [/color][color=#0000bb]int geta[/color][color=#007700]() {        return [/color][color=#0000bb]a[/color][color=#007700];    }[/color][color=#ff8000]// method geta.      [/color][color=#007700]public [/color][color=#0000bb]int getb[/color][color=#007700](){        return [/color][color=#0000bb]b[/color][color=#007700];    }[/color][color=#ff8000]//method getb.      [/color][color=#007700]public [/color][color=#0000bb]void change[/color][color=#007700](){        try {            if([/color][color=#0000bb]a[/color][color=#007700]==[/color][color=#0000bb]0 [/color][color=#007700]&& [/color][color=#0000bb]b[/color][color=#007700]==[/color][color=#0000bb]0[/color][color=#007700]){                [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"phuong trinh co vo so nghiem! "[/color][color=#007700]);            }else if([/color][color=#0000bb]a[/color][color=#007700]==[/color][color=#0000bb]0 [/color][color=#007700]&& [/color][color=#0000bb]b[/color][color=#007700]!=[/color][color=#0000bb]0[/color][color=#007700]){                [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"phuong trinh vo nghiem! "[/color][color=#007700]);            }else {                [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nghiem pt: " [/color][color=#007700]+ ((float) (-[/color][color=#0000bb]b[/color][color=#007700]/[/color][color=#0000bb]a[/color][color=#007700])) );            }                  } catch([/color][color=#0000bb]exception e[/color][color=#007700]){            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error here! " [/color][color=#007700]+[/color][color=#0000bb]e[/color][color=#007700]);        }    }[/color][color=#ff8000]//method change!      [/color][color=#007700]public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string args [/color][color=#007700][]){        [/color][color=#0000bb]trycatch a [/color][color=#007700]= new [/color][color=#0000bb]trycatch[/color][color=#007700]();        [/color][color=#0000bb]a[/color][color=#007700].[/color][color=#0000bb]setab[/color][color=#007700]();        [/color][color=#0000bb]a[/color][color=#007700].[/color][color=#0000bb]change[/color][color=#007700]();    }[/color][color=#ff8000]// method main.[/color][color=#007700]}[/color] 

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bài này của bạn ở phương thức change thì hình như ko nhảy vào catch đc nhỉ, vì lỗi là a==0 và b!=0 thì nó nhảy và chỗ if else rùi

[Quế Việt Nam]

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package ede[/color][color=#007700].[/color][color=#0000bb]cacbt[/color][color=#007700].[/color][color=#0000bb]kien[/color][color=#007700]; [/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]inputmismatchexception[/color][color=#007700];[/color][color=#0000bb]import java[/color][color=#007700].[/color][color=#0000bb]util[/color][color=#007700].[/color][color=#0000bb]scanner[/color][color=#007700]; public class [/color][color=#0000bb]trycatchbt [/color][color=#007700]{    public static [/color][color=#0000bb]void main[/color][color=#007700]([/color][color=#0000bb]string[/color][color=#007700][] [/color][color=#0000bb]args[/color][color=#007700]) {        [/color][color=#0000bb]scanner nhap [/color][color=#007700]= new [/color][color=#0000bb]scanner[/color][color=#007700]([/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]in[/color][color=#007700]);         try {            [/color][color=#0000bb]int a[/color][color=#007700];            [/color][color=#0000bb]int b[/color][color=#007700];             [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nhap a:  "[/color][color=#007700]);            [/color][color=#0000bb]a [/color][color=#007700]= [/color][color=#0000bb]nhap[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"nhap b:  "[/color][color=#007700]);            [/color][color=#0000bb]b [/color][color=#007700]= [/color][color=#0000bb]nhap[/color][color=#007700].[/color][color=#0000bb]nextint[/color][color=#007700]();             [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"ngiem la  :" [/color][color=#007700]+ (-[/color][color=#0000bb]b [/color][color=#007700]/ [/color][color=#0000bb]a[/color][color=#007700]));         } catch ([/color][color=#0000bb]arithmeticexception e[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error=  :" [/color][color=#007700]+ [/color][color=#0000bb]e[/color][color=#007700]);         } catch ([/color][color=#0000bb]inputmismatchexception e1[/color][color=#007700]) {            [/color][color=#0000bb]system[/color][color=#007700].[/color][color=#0000bb]out[/color][color=#007700].[/color][color=#0000bb]println[/color][color=#007700]([/color][color=#dd0000]"error nhap sai kieu du lieu: " [/color][color=#007700]+ [/color][color=#0000bb]e1[/color][color=#007700]);        }    } }[/color] 

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bài này hình như không liên quan đến hướng đối tượng nhỉ