重载、多态、接口
多态调用的顺序
当父类，和子类有Static时，先初始化Static，再初始化子类的Static，再初始化父类的其他成员变量－>父类构造方法－>子类其他成员变量－>子类的构造方法。
重写 hashcode equals compareto
Employee.java
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Objects;
public class Employee implements Comparable<Employee> {
private String name;
private double salary;
private Date hireDay;
public Employee(String n,
double s,
int year,
int month,
int day) {
name = n;
salary = s;
GregorianCalendar calendar =
new GregorianCalendar(year, month -
1, day);
hireDay = calendar.getTime();
}
public String
getName() {
return name;
}
public double getSalary() {
return salary;
}
public Date
getHireDate() {
return hireDay;
}
public boolean equals(Object Otherobject) {
if (
this == Otherobject)
return true;
if (Otherobject ==
null)
return false;
if (getClass() != Otherobject.getClass())
return false;
Employee other = (Employee) Otherobject;
return Objects.equals(name, other.name) && salary == other.salary && Objects.equals(hireDay, other.hireDay);
}
public int hashCode() {
return Objects.hash(name, salary);
}
public String
toString() {
return getClass().getName() +
"name=" + name +
",salary=" + salary +
",hireDay=" + hireDay;
}
@Override
public int compareTo(Employee other) {
return Double.compare(salary, other.salary);
}
}
Manager.java
public class Manager extends Employee {
private double bonus;
public Manager(String n,
double s,
int year,
int month,
int day) {
super(n, s, year, month, day);
bonus =
0;
}
public void setBonus(
double b) {
bonus = b;
}
@Override
public double getSalary() {
double baseSalary =
super.getSalary();
return bonus + baseSalary;
}
@Override
public boolean equals(Object Otherobject) {
if (!
super.equals(Otherobject))
return false;
Manager other = (Manager) Otherobject;
return bonus == other.bonus;
}
@Override
public int hashCode() {
return super.hashCode() +
17 *
new Double(bonus).hashCode();
}
@Override
public String
toString() {
return super.toString() +
",bonus=" + bonus;
}
}
异常
涉及return finally 以及异常抛出的问题
各个异常出现的情况
package exp;
import java.awt.Font;
import java.awt.FontFormatException;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.beans.Statement;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.Stack;
public class AllExcept {
public static void main(String[] args)
throws Exception {
try {
int[] s =
null;
int i = s.length;
}
catch (Exception e) {
System.out.println(
"1、" + e.getClass().getName() +
"异常");
}
try {
int[] s1 =
new int[
2];
s1[
2] =
5;
}
catch (Exception e) {
System.out.println(
"2、" + e.getClass().getName() +
"异常");
}
try {
Object x[] =
new String[
3];
x[
0] =
new Integer(
0);
}
catch (Exception e) {
System.out.println(
"3、" + e.getClass().getName() +
"异常");
}
try {
int a =
0;
int b =
10;
b /= a;
}
catch (Exception e) {
System.out.println(
"4、" + e.getClass().getName() +
"异常");
}
try {
String s2 =
"19k";
int n = Integer.parseInt(s2);
}
catch (Exception e) {
System.out.println(
"5、" + e.getClass().getName() +
"异常");
}
try {
StringBuffer buffer =
new StringBuffer();
buffer.charAt(
5);
}
catch (Exception e) {
System.out.println(
"6、" + e.getClass().getName() +
"异常");
}
try {
int i = -
1;
int[] s =
new int[i];
}
catch (Exception e) {
System.out.println(
"7、" + e.getClass().getName() +
"异常");
}
try {
String a =
"\\";
String a1 =
"\\.";
String[] x5 =
"abc.cde".split(a1);
x5 =
"abc.cde".split(a);
}
catch (Exception e) {
System.out.println(
"8、" + e.getClass().getName() +
"异常");
}
try {
Stack s =
new Stack();
s.pop();
}
catch (Exception e) {
System.out.println(
"9、" + e.getClass().getName() +
"异常");
}
try {
Object s = Class.forName(
"ClassName");
}
catch (Exception e) {
System.out.println(
"10、" + e.getClass().getName() +
"异常");
}
try {
Font f =
new Font(
"楷体", Font.BOLD,
7);
f.createFont(
2,
new File(
"1.txt"));
}
catch (FontFormatException e) {
System.out.println(
"11、" + e.getClass().getName());
}
catch (IllegalArgumentException e) {
System.out.println(
"12、" + e.getClass().getName() +
"异常");
}
try {
Image img = Toolkit.getDefaultToolkit().getImage(
"Images\1.jpg");
Graphics g = img.getGraphics();
g.drawRect(-
1, -
1, -
1, -
1);
}
catch (Exception e) {
System.out.println(
"13、" + e.getClass().getName() +
"异常");
}
try {
int cap =
2;
ByteBuffer bf = ByteBuffer.allocate(cap);
for (
int i =
0; i < cap; i++) {
bf.put((
byte) i);
}
bf.put((
byte)
10);
bf.getInt(
9);
}
catch (Exception e) {
System.out.println(
"14、" + e.getClass().getName() +
"异常");
}
try {
File f =
new File(
"E:\\1.txt");
byte[] buff =
new byte[
2];
FileInputStream file =
new FileInputStream(f);
int bytes = file.read(buff,
0,
2);
System.out.println(
new String(buff,
0,
0, bytes));
file.close();
}
catch (FileNotFoundException e) {
System.out.println(
"15、" + e.getClass().getName() +
"异常");
}
catch (EOFException e) {
System.out.println(
"16、" + e.getClass().getName() +
"异常");
}
catch (IOException e) {
System.out.println(
"17、" + e.getClass().getName() +
"异常");
}
try {
Object s =
new Integer(
0);
System.out.println((String) s);
}
catch (Exception e) {
System.out.println(
"18、" + e.getClass().getName() +
"异常");
}
try {
ByteBuffer buf = ByteBuffer.allocate(
50);
buf.flip();
byte[] byt =
new byte[
100];
buf.get(byt);
new RuntimeException();
}
catch (Exception e) {
System.out.println(
"19、" + e.getClass().getName() +
"异常");
}
try {
String sql =
"select * from Table";
Connection conn = DriverManager.getConnection(
"com.mysql.jdbc.Driver");
Statement smt = (Statement) conn.createStatement();
smt.execute();
}
catch (Exception e) {
System.out.println(
"20、" + e.getClass().getName() +
"异常");
}
}
}
工具
git svn 的 区别 和 常用命令
Maven依赖中的scope
测试
JUnit
Die.java
public class Die
{
private int faceValue;
private int numofsides;
public Die(){
faceValue =
0;
numofsides =
6;
}
public Die(
int v){
numofsides = v;
}
public int numOfSides(){
return numofsides;
}
public int topFace(){
return faceValue;
}
public void roll() {
faceValue = (
int) (
1 + Math.random() * numofsides );
}
}
TestDie.java
import org.junit.After;
import org.junit.Assert;
import org.junit.Test;
import org.junit.Before;
/**
* Unit test for simple App.
*/
public class TestDie {
private Die die1,die2;
@Before
public void setUp() {
die1 =
new Die();
die2 =
new Die(
10);
die1.roll();
die2.roll();
}
@Test
public void testdie1numofsides() {
Assert.assertEquals(
6, die1.numOfSides());
}
@Test
public void testdie1Face() {
Assert.assertTrue(die1.topFace() >=
1 && die1.topFace() <=
6);
}
@Test
public void testdie2numofsides() {
Assert.assertEquals(
10, die2.numOfSides());
}
@Test
public void testdie2Face() {
Assert.assertTrue(die2.topFace() >=
1 && die2.topFace() <=
10);
}
@After
public void tearDown() {
}
}
实现 assertEquals aseertSame
assertEquals.java
当expected和actual都是String类型时，ComparisonFailure还会找出是前后相同的串，并用[Different String]标明那些不相同的字符串，也就是expectedToString和actualToString的格式将会变成：…${sameString}[${differentString}]${sameString}…。其中“…”只会在相同的字符串太长的情况下才会出现，这个长度标准目前（JUnit4.10）是20个字符。具体实现参考ComparisonFailure类，它继承自AssertionError，这里不再展开。
/**
* Asserts that two objects are equal. If they are not, an
* {@link AssertionError} is thrown with the given message. If
* <code>expected</code> and <code>actual</code> are <code>null</code>,
* they are considered equal.
*
* @param message
* the identifying message for the {@link AssertionError} (<code>null</code>
* okay)
* @param expected
* expected value
* @param actual
* actual value
*/
static public void assertEquals(String message, Object expected,
Object actual) {
if (expected ==
null && actual ==
null)
return;
if (expected !=
null && isEquals(expected, actual))
return;
else if (expected
instanceof String && actual
instanceof String) {
String cleanMessage= message ==
null ?
"" : message;
throw new ComparisonFailure(cleanMessage, (String) expected,
(String) actual);
}
else
failNotEquals(message, expected, actual);
}
private static boolean isEquals(Object expected, Object actual) {
return expected.equals(actual);
}
/**
* Asserts that two objects are equal. If they are not, an
* {@link AssertionError} without a message is thrown. If
* <code>expected</code> and <code>actual</code> are <code>null</code>,
* they are considered equal.
*
* @param expected
* expected value
* @param actual
* the value to check against <code>expected</code>
*/
static public void assertEquals(Object expected, Object actual) {
assertEquals(
null, expected, actual);
}
aseertSame.java
/**
* Asserts that two objects refer to the same object. If they are not, an
* {@link AssertionError} is thrown with the given message.
*
* @param message
* the identifying message for the {@link AssertionError} (<code>null</code>
* okay)
* @param expected
* the expected object
* @param actual
* the object to compare to <code>expected</code>
*/
static public void assertSame(String message, Object expected, Object actual) {
if (expected == actual)
return;
failNotSame(message, expected, actual);
}
/**
* Asserts that two objects refer to the same object. If they are not the
* same, an {@link AssertionError} without a message is thrown.
*
* @param expected
* the expected object
* @param actual
* the object to compare to <code>expected</code>
*/
static public void assertSame(Object expected, Object actual) {
assertSame(
null, expected, actual);
}
其他
hamcrest 可以用来增强 JUnit 中的 assert 功能Cobertura is a free Java tool that calculates the percentage of code accessed by tests.stub & mock. EasyMock has been the first dynamic Mock Object generator, relieving users of hand-writing Mock Objects, or generating code for themDbUnit is a JUnit extension (also usable with Ant) targeted at database-driven projects that,among other things, puts your database into a known state between test runs
本文转自：http://blog.csdn.net/u011239443/article/details/53150159
