目录
1.Collection
1.1概念
//Collection
Collection cArray = new ArrayList();
//add
cArray.add("HELLO");
cArray.add(8);
System.out.println(cArray);
System.out.println("Is contains:HELLO -" + cArray.contains("HELLO"));
1.1遍历方法-Lambda表达式
1.2遍历方法-Iterator接口
注意：
1.3使用Lambda方法遍历Iterator接口
1.4使用Foreach方法遍历
代码示例：
public static void main(String[] args) {
//Collection
Collection cArray = new ArrayList();
//add
cArray.add("HELLO");
cArray.add(8);
System.out.println(cArray);
System.out.println("Is contains:HELLO -" + cArray.contains("HELLO"));
//Lambda
cArray.forEach(sy->System.out.println("Lambda:" + sy));
//Iterator
Iterator iter = cArray.iterator();
while (iter.hasNext()) {
String s = (String)iter.next();
System.out.println("Iterator:" + iter.next());
//Error
//cArray.remove(s);
}
//Lambda-Iterator
Iterator i = cArray.iterator();// define a new Iterator, can not use iter
i.forEachRemaining(obj->System.out.println("Lambda-Iterator:" + obj));
//foreach
for(Object value:cArray)
{
System.out.println("foreach:" + value);
}
}
1.5Predicate方法
public static void main(String[] args) {
//Collection
Collection cArray = new ArrayList();
//add
cArray.add("HELLO");
cArray.add("8");
cArray.add("aaa8");
System.out.println("Init:" + cArray);
System.out.println("Is contains:HELLO -" + cArray.contains("HELLO"));
//Predicate
cArray.removeIf(obj->((String)obj).length()<3); //remove length less than 3
cArray.removeIf(obj->((String)obj).contains("8")); //remove contains 8
System.out.println("After removeIf:" + cArray);
}
2.一个常用类和集合的简单例子：账号密码登录
package per.liyue.code.login;
public class User {
private int id;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
private String passWord;
public String getPassWord() {
return passWord;
}
public void setPassWord(String passWord) {
this.passWord = passWord;
}
@Override
public String toString() {
// TODO Auto-generated method stub
return "用户名：" + this.id + " 密码：" + this.passWord;
}
@Override
public boolean equals(Object obj) {
// TODO Auto-generated method stub
User user = (User)obj;
if ((user.id == this.id)) {
return true;
} else {
return false;
}
}
}
package per.liyue.code.login;
import java.util.ArrayList;
import java.util.Collection;
import java.util.InputMismatchException;
import java.util.Iterator;
import java.util.Scanner;
public class Init {
//static Scanner scanner = new Scanner(System.in);
static Collection users = new ArrayList<>();
public static void main(String[] args) {
// TODO Auto-generated method stub
while (true) {
System.out.println("请选择 A[注册] B[登录] C[退出]");
String option = getMyScanner().next();
// 注册
if ("a".equalsIgnoreCase(option)) {
User userNew = new User();
try {
reg(userNew);
} catch (InputMismatchException e) {
System.out.println("账号只能为数字类型，请重新输入：");
reg(userNew);
}
System.out.println("注册成功！");
users.add(userNew);
printUser();
}
// 登录
else if ("b".equalsIgnoreCase(option)) {
try {
login();
} catch (InputMismatchException e) {
System.out.println("账号只能为数字类型，请重新输入：");
login();
}
} else if ("c".equalsIgnoreCase(option)) {
System.out.println("退出系统！");
System.exit(0);
} else {
System.out.println("请输入正确的字母！");
}
} // while
// true
}
public static void reg(User userNew) throws InputMismatchException {
// id
while (true) {
System.out.println("请输入账号:");
int id = getMyScanner().nextInt();
if (users.contains(id)) {
System.out.println("账号已经存在，请重新输入！");
} else {
userNew.setId(id);
break;
}
} // while true id
// password
System.out.println("请输入密码,输入C返回菜单");
String passWord = getMyScanner().next();
userNew.setPassWord(passWord);
}
public static void printUser() {
Iterator iterator = users.iterator();
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.toString());
}
}
public static void login() throws InputMismatchException {
while (true) {
System.out.println("请输入账号");
User userLog = new User();
userLog.setId(getMyScanner().nextInt());
System.out.println("请输入密码,输入C返回菜单：");
userLog.setPassWord(getMyScanner().next());
Iterator iterator = users.iterator();
boolean checkExists = false;
while (iterator.hasNext()) {
User user = (User) iterator.next();
if (user.equals(userLog)) {
checkExists = true;
}
}
if (checkExists) {
System.out.println("登录成功！");
} else {
System.out.println("请输入正确的账号密码！");
}
}
}
public static Scanner getMyScanner(){
return new Scanner(System.in);
}
}