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);
    }
}