학원 6일차 복습(3/21)

이론

오류의 종류: 에러,예외

예외의 종류: 컴파일 예외, 런타임예외

예외(exception): 잘못된 코드, 부정확한 데이터, 예외적인 상황에 의하여 발생하는 오류

예외 처리: try-catch-finally , throws

오류가 발생하였건 발생하지 않았건 항상 실행되어야 하는 코드는 finally 블록에 넣을 수 있다.

throws: 예외 떠넘기기

getMessage(): 예외 발생시킬 때 생성자 매개값으로 사용한 메시지 리턴

printStackTrace(): 예외 발생 코드 추적한 내용을 모두 콘솔에 출력 , 오류 찾을 때 유용하게 활용

list:    순서유지, 중복저장

set:    순서X, 중복X, null은 허용

map:    키값가짐, 키는 set을 따름(중복X)

실습

ex1.Ex0_ArrayIndex

package ex1; import java.util.Scanner; public class Ex0_ArrayIndex { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String[] str = new String[3]; for(int i=0; i<3;i++){ System.out.print("문자"+(i+1)+":"); str[i]= sc.nextLine(); } for(int i = 0; i<=str.length; i++){ System.out.println(str[i]); System.out.println("-------------"); } } }

ex1.Ex1.NullPoint

package ex1; public class Ex1_NullPoint { public void test(){ System.out.println("Test"); } public static void main(String[] args) { Ex1_NullPoint en = null; try{ en.test(); //예외가 발생하는 문장, 예외가 발생하면 발생한 실행문에서 //catch로 넘어간다. System.out.println("테스트가 호출한 이후의 실행문!"); }catch(NullPointerException e){ // catch로 간다. System.out.println("객체는 생성되어야 한다."); //Exception에서 예외메세지 출력 e.printStackTrace(); } } }

ex1.Ex2.ArrayIndexException

package ex1; import java.util.Scanner; public class Ex2_ArrayIndexException { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("숫자 입력: "); String number = sc.nextLine(); String[] argsv = {"10", number, "30"}; try{ for(int i = 0; i<= argsv.length; i++){//1 int n = Integer.parseInt(argsv[i]); System.out.println(n); System.out.println("-------------****");//예외발생시 수행안됨! } }catch(NumberFormatException | ArrayIndexOutOfBoundsException e){ System.out.println("숫자를 입력 발생"); }finally{//무조건 실행! 특정 리소스를 반환하는 메서드를 호출할때 사용 System.out.println("여기는 예외와 상관없이 무조건 수행이됨!"); } } }

ex1.Ex3.MultiException

package ex1; import java.util.Scanner; public class Ex3_MultiException { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("숫자 입력 : "); try{ int number = Integer.parseInt(sc.nextLine()); int result = 0; for (int i = 0; i<10; i++){ //아래의 예외처리에서 멀티 Exception을 처리하시오. result = number / (int)(Math.random()*5); System.out.println(result); }//for의 마지막 }catch(NumberFormatException | ArithmeticException e){ e.printStackTrace(); //분석, NumberFormatException , ArithmeticException // instanceof를 사용해서 같은 메모리영역에(부모,자식,그 해당객체인지)같은 주소인지 //판별해주는 도구 if(e instanceof NumberFormatException){ System.out.println("숫자발생"); }else{ System.out.println("예외 발생"); } }catch(Exception e){ System.out.println("나머지 예외!"); }// try-catch의 마지막 } }

ex1.Ex5.ThrowView

package ex1; public class Ex5_ThrowView { public static void main(String[] args) { try{ findClass(); }catch(ClassNotFoundException ex){ System.out.println("예외 처리 가능!"); } } //------------------------------------------- //예) findClass 메서드는 다른 클래스에서 정의되었다고 가정! // throws를 사용해서 호출한 곳으로 위임! // throws ClassNotFoundException public static void findClass() throws ClassNotFoundException{ // try{ // forName("") : 문자열로 지정된 경로의 클래스를 불러온다. Class clazz = Class.forName("java.lang.String2"); // }catch(ClassNotFoundException ex){ // System.out.println("예외 형식"); // } } }

ex1.Ex6.UserException

package ex1; //사용자 정의 예외처리 extends Exception 상속받아서 //예외를 처리 할 수 도 있다. public class Ex6_UserException extends Exception{ private int port = 772; public Ex6_UserException(String message){ super(message); // 부모의 생성자를 호출! } public Ex6_UserException(String msg, int port){ super(msg); this.port= port; } public int getPort() { return port; } }

ex1.Ex6.UserExceptionTest

package ex1; public class Ex6_UserExceptionTest { public void test(String[] n) throws Ex6_UserException{ System.out.println("Test1"); if(n.length <3){ //throw는 강제 예외를 생성해서 발생 //테스트할 때 자주 사용! throw new Ex6_UserException("없음"); }else{ throw new Ex6_UserException("최종예선",703); } } public static void main(String[] args) { Ex6_UserExceptionTest ex = new Ex6_UserExceptionTest(); try{ // String API에서 가지고 있는 메서드(반환형이 String 배열) // OK/AA/BB-> "/"를 기준으로 배열로 저장해서 반환 String[] ar = "ok/aa/".split("/"); System.out.println("ar : length"+ar.length); ex.test(ar); }catch(Ex6_UserException e){ e.printStackTrace(); } } }

ex1.exam.Exam1_Exception

package ex1.exam; import java.util.Scanner; public class Exam1_Exception { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("숫자 입력 : "); try{ int number = Integer.parseInt(sc.nextLine()); int result = 0; for (int i = 0; i<10; i++){ result = number / (int)(Math.random()*5); System.out.println(result); } }catch(NumberFormatException e){ System.out.println("숫자를 입력 발생"); }catch(ArithmeticException e){ System.out.println("0으로 나눌수 없습니다."); }catch(Exception e){ System.out.println("알수 없는 예외!"); }finally{ System.out.println("여기는 예외와 상관없이 무조건 수행이됨!"); } } }

ex1.exam.Exam2_Exception

package ex1.exam; // throws를 사용해서 예외처리 해보기 import java.util.logging.Level; import java.util.logging.Logger; public class Exam2_Exception { public static void test() throws ArithmeticException{ System.out.println(6 / 0); System.out.println("냠냠! "); } public static void main(String[] args) { Exam2_Exception ref = new Exam2_Exception(); try { ref.test(); } catch (ArithmeticException e) { System.out.println("0으로 나눌수 없습니다"); } } }

ex2.Ex0.GuiTest

/* * 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. */ package ex2; import java.awt.Color; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JButton; /** * event 처리하기 위해서는 이벤트 감지자가 필요하다. * XXListener 인페이스 제공받는다.(추상메서드를 가지고 있기 때문이다.) */ //1.발생하는 이벤트의 종류를 파악한 후 이벤트처리 인터페이스를 구현하는 방법 public class Ex0_GuiTest extends javax.swing.JFrame implements ActionListener{ /** * Creates new form Ex0_GuiTest */ public Ex0_GuiTest() { initComponents(); //GUI객체를 정의하거나 호출한 메서드 // 3.버튼에 이벤트 감지자를 등록 해놔야 한다. // p2의 배경색을 변경 p2.setBackground(Color.blue); btn1.addActionListener(this); btn2.addActionListener(this); btn3.addActionListener(this); } /** * This method is called from within the constructor to initialize the form. * WARNING: Do NOT modify this code. The content of this method is always * regenerated by the Form Editor. */ @SuppressWarnings("unchecked") // <editor-fold defaultstate="collapsed" desc="Generated Code"> private void initComponents() { p1 = new javax.swing.JPanel(); btn1 = new javax.swing.JButton(); btn2 = new javax.swing.JButton(); btn3 = new javax.swing.JButton(); p2 = new javax.swing.JPanel(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); btn1.setBackground(new java.awt.Color(255, 51, 51)); btn1.setText("Red"); btn1.addActionListener(new java.awt.event.ActionListener() { public void actionPerformed(java.awt.event.ActionEvent evt) { btn1ActionPerformed(evt); } }); btn2.setBackground(new java.awt.Color(51, 255, 102)); btn2.setText("Green"); btn3.setBackground(new java.awt.Color(102, 255, 255)); btn3.setText("Blue"); javax.swing.GroupLayout p1Layout = new javax.swing.GroupLayout(p1); p1.setLayout(p1Layout); p1Layout.setHorizontalGroup( p1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(p1Layout.createSequentialGroup() .addGap(114, 114, 114) .addComponent(btn1, javax.swing.GroupLayout.PREFERRED_SIZE, 85, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(169, 169, 169) .addComponent(btn2, javax.swing.GroupLayout.PREFERRED_SIZE, 85, javax.swing.GroupLayout.PREFERRED_SIZE) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 184, Short.MAX_VALUE) .addComponent(btn3, javax.swing.GroupLayout.PREFERRED_SIZE, 85, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(76, 76, 76)) ); p1Layout.setVerticalGroup( p1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, p1Layout.createSequentialGroup() .addContainerGap(40, Short.MAX_VALUE) .addGroup(p1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(btn1, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(btn2, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(btn3, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE)) .addGap(33, 33, 33)) ); p2.setBackground(new java.awt.Color(255, 255, 0)); javax.swing.GroupLayout p2Layout = new javax.swing.GroupLayout(p2); p2.setLayout(p2Layout); p2Layout.setHorizontalGroup( p2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGap(0, 0, Short.MAX_VALUE) ); p2Layout.setVerticalGroup( p2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGap(0, 312, Short.MAX_VALUE) ); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(p1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addComponent(p2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addComponent(p1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addComponent(p2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)) ); pack(); }// </editor-fold> private void btn1ActionPerformed(java.awt.event.ActionEvent evt) { // TODO add your handling code here: } /** * @param args the command line arguments */ public static void main(String args[]) { /* Set the Nimbus look and feel */ //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) "> /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html */ try { for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { if ("Nimbus".equals(info.getName())) { javax.swing.UIManager.setLookAndFeel(info.getClassName()); break; } } } catch (ClassNotFoundException ex) { java.util.logging.Logger.getLogger(Ex0_GuiTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (InstantiationException ex) { java.util.logging.Logger.getLogger(Ex0_GuiTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (IllegalAccessException ex) { java.util.logging.Logger.getLogger(Ex0_GuiTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (javax.swing.UnsupportedLookAndFeelException ex) { java.util.logging.Logger.getLogger(Ex0_GuiTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } //</editor-fold> /* Create and display the form */ java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Ex0_GuiTest().setVisible(true); } }); } // Variables declaration - do not modify private javax.swing.JButton btn1; private javax.swing.JButton btn2; private javax.swing.JButton btn3; private javax.swing.JPanel p1; private javax.swing.JPanel p2; // End of variables declaration @Override public void actionPerformed(ActionEvent e) { // Action이벤트가 발생 한 후 동작될 작업을 이곳에 정의한다. System.out.println("click ! 메서드가 호출 되었습니다."); //각각의 버튼 감지자에 의해서 클릭 될 때마다 발생하는 ActionEvent의 주소값 e //getSource() 선택된 JButton의 주소값을 받아옴 JButton btn = (JButton) e.getSource(); if(btn == btn1){ System.out.println("첫번째 버튼 클릭!!!"); }else if(btn == btn2){ System.out.println("두번째 버튼 클릭!!!"); }else if(btn == btn3){ System.out.println("세번째 버튼 클릭!!!"); } p2.setBackground(btn.getBackground()); } }

ex2.Ex0.Num

/* package ex2; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class Ex0_Num extends javax.swing.JFrame { /** * Creates new form Ex0_Num */ int num; public Ex0_Num() { initComponents(); //익명내부클래스를 사용해서 이벤트를 처리함! btn1.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { System.out.println("+ 버튼이 클릭!"); result.setText("Num:" + (++num)); } }); btn2.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { System.out.println("- 버튼이 클릭!"); if (num > 0) { result.setText("Num:" + (--num)); } } }); } /** * This method is called from within the constructor to initialize the form. * WARNING: Do NOT modify this code. The content of this method is always * regenerated by the Form Editor. */ @SuppressWarnings("unchecked") // <editor-fold defaultstate="collapsed" desc="Generated Code"> private void initComponents() { jPanel1 = new javax.swing.JPanel(); jButton1 = new javax.swing.JButton(); btn1 = new javax.swing.JButton(); btn2 = new javax.swing.JButton(); text = new javax.swing.JTextField(); result = new javax.swing.JLabel(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); jPanel1.setBackground(new java.awt.Color(153, 153, 255)); jButton1.setText("입력"); jButton1.addActionListener(new java.awt.event.ActionListener() { public void actionPerformed(java.awt.event.ActionEvent evt) { jButton1ActionPerformed(evt); } }); btn1.setText("+"); btn2.setText("-"); result.setFont(new java.awt.Font("굴림", 0, 24)); // NOI18N result.setText("Num:0"); javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1); jPanel1.setLayout(jPanel1Layout); jPanel1Layout.setHorizontalGroup( jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(jPanel1Layout.createSequentialGroup() .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addComponent(text, javax.swing.GroupLayout.PREFERRED_SIZE, 216, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(61, 61, 61) .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 94, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(18, 18, 18) .addComponent(btn1, javax.swing.GroupLayout.PREFERRED_SIZE, 86, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(43, 43, 43) .addComponent(btn2, javax.swing.GroupLayout.PREFERRED_SIZE, 95, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(75, 75, 75)) .addGroup(jPanel1Layout.createSequentialGroup() .addGap(442, 442, 442) .addComponent(result, javax.swing.GroupLayout.PREFERRED_SIZE, 287, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap(201, Short.MAX_VALUE)) ); jPanel1Layout.setVerticalGroup( jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(jPanel1Layout.createSequentialGroup() .addGap(71, 71, 71) .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(btn1, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(btn2, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(text, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE)) .addGap(146, 146, 146) .addComponent(result, javax.swing.GroupLayout.PREFERRED_SIZE, 81, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap(222, Short.MAX_VALUE)) ); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) ); pack(); }// </editor-fold> private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { // TODO add your handling code here: } /** * @param args the command line arguments */ public static void main(String args[]) { /* Set the Nimbus look and feel */ //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) "> /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html */ try { for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { if ("Nimbus".equals(info.getName())) { javax.swing.UIManager.setLookAndFeel(info.getClassName()); break; } } } catch (ClassNotFoundException ex) { java.util.logging.Logger.getLogger(Ex0_Num.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (InstantiationException ex) { java.util.logging.Logger.getLogger(Ex0_Num.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (IllegalAccessException ex) { java.util.logging.Logger.getLogger(Ex0_Num.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (javax.swing.UnsupportedLookAndFeelException ex) { java.util.logging.Logger.getLogger(Ex0_Num.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } //</editor-fold> /* Create and display the form */ java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Ex0_Num().setVisible(true); } }); } // Variables declaration - do not modify private javax.swing.JButton btn1; private javax.swing.JButton btn2; private javax.swing.JButton jButton1; private javax.swing.JPanel jPanel1; private javax.swing.JLabel result; private javax.swing.JTextField text; // End of variables declaration }

ex2.Ex1.ArrayList

package ex2; import java.util.ArrayList; public class Ex1_ArrayList { public static void main(String[] args) { ArrayList ar = new ArrayList(); System.out.println("사이즈1: "+ar.size()); //ArrayList에 값을 저장해보기 ar.add("Test"); //0 ar.add("Test"); //1 int num = 200; ar.add(num);//2 Character ch = 'A'; ar.add(ch); ar.add(3.11f); ar.add(100L); System.out.println("사이즈2: "+ar.size()); // 배열과 마찬가지로 첫번째 요소의 인덱스는 0이다. for(int i = 0; i<ar.size(); i++){ //get(index)메서드를 사용해서 요소의 값 가져오기 System.out.println(ar.get(i)); } System.out.println("----------------------"); //향상된 for문으로 변경해보기 for(Object e : ar){ if(e instanceof String){ System.out.println("Str: "+e); }else if(e instanceof Integer){ System.out.println("Int: "+e); }else if(e instanceof Character){ System.out.println("Char: "+e); }else if(e instanceof Float){ System.out.println("Float: "+e); }else if(e instanceof Long){ System.out.println("Long: "+e); } } for(Object e : ar){ String str = e.getClass().getTypeName(); String str2 = e.getClass().getSimpleName(); System.out.println(str); System.out.println("str2: "+str2); //substring 문자열 자르는 메서드 *** String 반환 //lastIndexOf(".") - 마지막 .을 기준으로 문자열의 위치를 반환 - int형 //java.lang.String System.out.println(str.substring(str.lastIndexOf(".")+ 1)+"형 :"+e); } System.out.println("----------------------"); //String API학습하기..(조별학습) String test = "abcdef"; System.out.println(test.substring(1)); } }