JinLoveJava
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package lianxii;
import java.util.HashMap;
import java.util.Map;
public class MapExp {
public static void main(String[] args) {
// String s = "";一般字符串定义成这样
// String p1 = null;对象一般定义成这样
String s1 = "p";
Map<String, Object> ...
package lianxii;
import java.util.Date;
public class Person2 {
public String name;
public int age;
private Date birthDate;
public String getInfo() {
return "name:" + name + "\nage:" + age;
}
}
//类Person2
package lianxii;
public class Student2 ...
package lianxii;
import java.util.Date;
public class Person {
protected String name;
protected int age;
protected Date birthDate;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int get ...
package lianxii;
import java.util.Date;
public class Person {
protected String name;
protected int age;
protected Date birthDate;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int get ...
package lianxii;
class Parent {
private final int f1 = 1;
int f2 = 2;
protected int f3 = 3;
public int f4 = 4;
private void fm1() {
System.out.println(f1);
}
void fm2() {
System.out.println(f2);
}
protected void fm3() ...
package lianxii;
public class TestAnimals {
public static void main(String[] args) {
Horse b = new Horse();
System.out.println(b.getI());
// Animal b = new Animal();
// int yy = b.getI();
// System.out.println(yy);
}
}
class An ...
package lianxii;
import java.util.Locale;
public class Change {
public static void main(String[] args) {
String name = "i";
Locale loc = Locale.getDefault();//可以去掉这步
System.out.println("转换前：" + name);
System.out.println("转换后：" + na ...
package lianxii;
import java.util.Locale;
public class Local {
public static void main(String[] args) {
String str = "ThIs Is HaRd";
Locale loc = Locale.getDefault();//可以去掉这步
String lowerStr = str.toLowerCase(loc);
String upperStr = str.toUpperCase(lo ...
package lianxii;
public class Variable {
private int i = 1; //也可int i;
public void method1() {
int i = 4, j = 5;
this.i = i + j;
System.out.println(this.i);//使用当前定义的int i=1
method2(2);
}
public void method2(int i) {
int j = 8;
this ...
package lianxii;
public class Book {
private String title;
public void setTitle(String title1) {
title = title1;
}
public String getTitle() {
return title;
}
public static void main(String[] args) {
Book b = new Book();
b.setTitle(" ...
package lianxii;
public class Person {
public int age;
}
class Te {
public static void main(String[] args) {
Person t = new Person();
t.age = -3;
}
}
注：类class Te，去掉public正确
package lianxii;
public class Person {
public int age;
}
public class Te {
public static void main(String[] args) {
Person t = new Person();
t.age = -3;
}
}
注:加public报错
package lianxii;
public class Person {
public int age;
public static class Te {
public static void main(String[] args) {
Person t = new Person();
t.age = -3;
}
}
}
package lianxii;
public class Person {
public int age;
public class ...
一.历史原因:Hashtable是基于陈旧的Dictionary类的，HashMap是Java 1.2引进的Map接口的一个实现
二.同步性:Hashtable是线程安全的，也就是说是同步的，而HashMap是线程序不安全的，不是同步的
三.值：只有HashMap可以让你将空值作为一个表的条目的key或value
一个是存储单列数据的集合，另一个是存储键和值这样的双列数据的集合。
List中存储的数据是有顺序，并且允许重复；Map中存储的数据是没有顺序的，其键是不能重复的，它的值是可以有重复的。
set不允许有重复元素。