Java学习

P523 集合-使用Iterator遍历Collection

package com.collection;

import org.junit.Test;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class IteratorTest {
    
    @Test
    public void test1(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(456);
        coll.add(new Person("Jerry",20));
        coll.add(new String("Tom"));
        coll.add(false);
        Iterator iterator = coll.iterator();
        // next
//        System.out.println(iterator.next());
//        System.out.println(iterator.next());
//        System.out.println(iterator.next());
//        System.out.println(iterator.next());
//        System.out.println(iterator.next());

//        for (int i = 0; i < coll.size(); i++) {
//            System.out.println(iterator.next());
//        }
        // hasNext
        while(iterator.hasNext()){
            System.out.println(iterator.next());
        }
    }
}

P524 集合-迭代器Iterator的执行原理 P525 集合-迭代器Iterator遍历集合的两种错误写法

    @Test
    public void test2(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(456);
        coll.add(new Person("Jerry",20));
        coll.add(new String("Tom"));
        coll.add(false);
        Iterator iterator = coll.iterator();
        // 错误方式1
        while((iterator.next()) != null){
            System.out.println(iterator.next());
        }
        // 错误方式2
        while(coll.iterator().hasNext()){
            System.out.println(coll.iterator().next());
        }
    }

P526 集合-Iterator迭代器remove的使用

    @Test
    public void test3(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(456);
        coll.add(new Person("Jerry",20));
        coll.add(new String("Tom"));
        coll.add(false);
        Iterator iterator = coll.iterator();
        while (iterator.hasNext()){
            Object obj = iterator.next();
            if ("Tom".equals(obj)){
                iterator.remove();
            }
        }
        iterator = coll.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }
    }

P527 集合-新特性foreach循环遍历集合或项目

package com.collection;

import org.junit.Test;

import java.util.ArrayList;
import java.util.Collection;


public class ForTest {
    @Test
    public void test1(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(456);
        coll.add(new Person("Jerry",20));
        coll.add(new String("Tom"));
        coll.add(false);
        // 增强循环仍然调用了迭代器
        for (Object obj : coll) {
            System.out.println(obj);
        }
    }
    @Test
    public void test2(){
        int[] arr = new int[]{1,2,3,4,5,6};
        for (int i : arr) {
            System.out.println(i);
        }
    }
    @Test
    public void test3(){
        String[] arr = new String[]{"MM","MM","MM"};
        for (int i = 0; i < arr.length; i++) {
            arr[i] = "GG";
        }
        // 不变
        for (String s : arr) {
            s = "GG";
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
    }
}

P528 集合-List接口常用实现类的对比

package com.collection;


public class ListTest {
}

P529 集合-ArrayList的源码分析

P530 集合-LinkedList的源码分析

P531 集合-Vector的源码分析

// 现已基本不用
// 和ArrayList底层相似，初始化数组容量为10，扩容为原来的二倍，是线程安全的

P532 集合-List接口的常用方法测试

package com.collection;

import org.junit.Test;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


// List接口中的常用方法
public class ListTest {
    @Test
    public void test1(){
        ArrayList list = new ArrayList();
        list.add(123);
        list.add(456);
        list.add("AA");
        list.add(new Person("Tom",12));
        list.add(456);

        System.out.println(list);
        //add
        list.add(1,"BB");
        System.out.println(list);
        //addAll
        List list1 = Arrays.asList(1, 2, 3);
        list.addAll(list1);
        System.out.println(list.size());
        //get
        System.out.println(list.get(0));
    }
    @Test
    public void test2(){
        ArrayList list = new ArrayList();
        list.add(123);
        list.add(456);
        list.add("AA");
        list.add(new Person("Tom",12));
        list.add(456);
        // indexOf
        int i = list.indexOf(456);
        System.out.println(i);
        // remove
        Object obj = list.remove(0);
        System.out.println(obj);
        System.out.println(list);
        // set
        list.set(1,"CC");
        System.out.println(list);
        // subList
        List list1 = list.subList(1, 3);
        System.out.println(list1);
    }

}

P533 集合-List遍历及方法总结

    
    @Test
    public void test3(){
        ArrayList list = new ArrayList();
        list.add(123);
        list.add(456);
        list.add("AA");
        // 迭代器
        Iterator iterator = list.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }
        // 增强for循环
        for (Object obj : list) {
            System.out.println(obj);
        }
        // 普通for循环
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }