java list

list承诺可以将元素维护在特定的序列中,List接口在Collection的基础上添加了大量的方法,使得可以在List的中间插入和移动元素

有两种List

基本的ArrayList,它长于随机访问元素,但时在List的中间插入和移除元素较慢

LinkedList,它通过代价较低的在List中间进行的插入和删除操作,提供了优化的顺序访问.LinkedList在随机访问方面相对较慢,但它的特性较ArrayList更大

package java.util;

import java.util.function.UnaryOperator;
public interface List<E> extends Collection<E> {  
    int size();
    boolean isEmpty();//判断List是否为空
    boolean contains(Object o);  //确定某个对象是否在列表中

        //对于基本数据类型和 String类型 如果字面值一样将返回true
        //对于对象和包装类如果是新new 的一个对象,即使字面值一样也返回false

 Iterator<E> iterator(); //迭代器
Object[] toArray(); //创建一个合适的数组 
<T> T[] toArray(T[] a);//将 a转化为一个数组
 boolean add(E e);     //
boolean remove(Object o);//将对象引用传递给remove()方法移除一个对象 
boolean containsAll(Collection<?> c); //判断一个List列表是否被包含在里面
      
    boolean addAll(Collection<? extends E> c);//插入一个List列表
    boolean addAll(int index, Collection<? extends E> c);//插入一个对象
    boolean removeAll(Collection<?> c); //基于equals(),移除List中的所有c中所包含的元素
    boolean retainAll(Collection<?> c); //retainAll()方法是一种"交集"操作,retainAll()行为依赖于equals()
    default void replaceAll(UnaryOperator<E> operator) {
        Objects.requireNonNull(operator);
        final ListIterator<E> li = this.listIterator();
        while (li.hasNext()) {
            li.set(operator.apply(li.next()));
        }
    }
    @SuppressWarnings({"unchecked", "rawtypes"})
    default void sort(Comparator<? super E> c) {  //排序List //Collection类中shuffle()方法为随机打乱
        Object[] a = this.toArray();
        Arrays.sort(a, (Comparator) c);
        ListIterator<E> i = this.listIterator();
        for (Object e : a) {
            i.next();
            i.set((E) e);
        }
    }

    void clear();                       //清空List
    boolean equals(Object o);           //contains(),removeAll()和indexOf都会调用equals(),equals()属于Object的一部分
    //List的行为会根据equals()的行为有所变化
    int hashCode();
    E get(int index);           //返回Index所在的element
    E set(int index, E element);//和Set存在潜在冲突,该方法将index号元素修改为element
    void add(int index, E element);//添加element到index位置
    E remove(int index);        //移除Index所在的element
    int indexOf(Object o); //查找对象在List中所处的位置的索引编号(查找的是引用)
     //即使两个对象看起来一样也不相等,但是如果是基本数据类型则会相等
    int lastIndexOf(Object o);
    ListIterator<E> listIterator();
    ListIterator<E> listIterator(int index);
    List<E> subList(int fromIndex, int toIndex);//从一个大的List中创建一个片段(引用),不包括toIndex的值
    //修改片段将大导致的List列表被修改
    @Override
    default Spliterator<E> spliterator() {
        return Spliterators.spliterator(this, Spliterator.ORDERED);
    }
}

下面是一个Integer应用实例

package object;

//: holding/E05_IntegerListFeatures.java /****************** Exercise 5 ******************  * Use Integers instead of Pets to modify   * ListFeatures.java  (remember autoboxing).  * Explain any difference in results.  ***********************************************/  package holding; import java.util.*; import static net.mindview.util.Print.*; 
import java.util.*;
import static net.util.Print.*;

public class E05_IntegerListFeatures {
    static Random rand = new Random(47);

    public static void main(String[] args) {
        List<Integer> ints = new ArrayList<Integer>(
                Arrays.asList(1, 2, 3, 4, 5, 6, 7));
        print("1: " + ints);
        ints.add(8);
        print("2: " + ints);
        print("3: " + ints.contains(8));
        ints.remove(Integer.valueOf(8));
        Integer i = ints.get(2);
        print("4: " + i + " " + ints.indexOf(i));
        Integer j = Integer.valueOf(1);
        print("5: " + ints.indexOf(j));
        print("6: " + ints.remove(j));
        print("7: " + ints.remove(i));
        print("8: " + ints);
        ints.add(3, 0);
        print("9: " + ints);
        List<Integer> sub = ints.subList(1, 4);
        print("subList: " + sub);
        print("10: " + ints.containsAll(sub));
        Collections.sort(sub);
        print("sorted subList: " + sub);
        print("11: " + ints.containsAll(sub));
        Collections.shuffle(sub, rand);
        print("shuffled subList: " + sub);
        print("12: " + ints.containsAll(sub));
        List<Integer> copy = new ArrayList<Integer>(ints);
        sub = Arrays.asList(ints.get(1), ints.get(4));
        print("sub: " + sub);
        copy.retainAll(sub);
        print("13: " + copy);
        copy = new ArrayList<Integer>(ints);
        // Thinking in Java, 4th Edition Annotated Solution Guide 184
        copy.remove(2);
        print("14: " + copy);
        copy.removeAll(sub);
        print("15: " + copy);
        copy.set(1, 9);
        print("16: " + copy);
        copy.addAll(2, sub);
        print("17: " + copy);
        print("18: " + ints.isEmpty());
        ints.clear();
        print("19: " + ints);
        print("20: " + ints.isEmpty());
        ints.addAll(Arrays.asList(1, 2, 3, 4));
        print("21: " + ints);
        Object[] o = ints.toArray();
        print("22: " + o[3]);
        Integer[] ia = ints.toArray(new Integer[0]);
        print("22: " + ia[3]);
    }
} /*
     * Output: 1: [1, 2, 3, 4, 5, 6, 7] 2: [1, 2, 3, 4, 5, 6, 7, 8] 3: true 4: 3
     * 2 5: 0 6: true 7: true 8: [2, 4, 5, 6, 7] 9: [2, 4, 5, 0, 6, 7] subList:
     * [4, 5, 0] 10: true sorted subList: [0, 4, 5] 11: true shuffled subList:
     * [4, 0, 5] 12: true sub: [4, 6] 13: [4, 6] 14: [2, 4, 5, 6, 7] 15: [2, 5,
     * 7] 16: [2, 9, 7] 17: [2, 9, 4, 6, 7] 18: false 19: [] 20: true 21: [1, 2,
     * 3, 4] 22: 4 22: 4 Holding Your Objects 185
     */// :~

 String

package ch06;

//: holding/E05_StringListFeatures.java /****************** Exercise 5 ******************  * Use Strings instead of Pets to modify   * ListFeatures.java  (remember autoboxing).  * Explain any difference in results.  ***********************************************/  package holding; import java.util.*; import static net.mindview.util.Print.*; 
import java.util.*;
import static net.util.Print.*;

public class E05_StringListFeatures {
    static Random rand = new Random(47);

    public static void main(String[] args) {
        List<String> ints = new ArrayList<String>(
                Arrays.asList("dog", "pig", "duck", "fly", "event", "boast", "convince"));
        print("1: " + ints);
        ints.add("yes");
        print("2: " + ints);
        print("3: " + ints.contains("pig"));
        ints.remove(String.valueOf("pig"));
        String i = ints.get(2);
        print("4: " + i + " " + ints.indexOf(i));
        String j = String.valueOf("event");
        print("5: " + ints.indexOf(j));
         print("6: " + ints.remove(j));
        print("7: " + ints.remove(i));
        print("8: " + ints);
        ints.add(3, "no");
        print("9: " + ints);
        List<String> sub = ints.subList(1, 4);
        print("subList: " + sub);
        print("10: " + ints.containsAll(sub));
        Collections.sort(sub);
        print("sorted subList: " + sub);
        print("11: " + ints.containsAll(sub));
        Collections.shuffle(sub, rand);
        print("shuffled subList: " + sub);
        print("12: " + ints.containsAll(sub));
        List<String> copy = new ArrayList<String>(ints);
        sub = Arrays.asList(ints.get(1), ints.get(4));
        print("sub: " + sub);
        copy.retainAll(sub);
        print("13: " + copy);
        copy = new ArrayList<String>(ints);
        // Thinking in Java, 4th Edition Annotated Solution Guide 184
        copy.remove(2);
        print("14: " + copy);
        copy.removeAll(sub);
        print("15: " + copy);
        copy.set(1, "connect");
        print("16: " + copy);
        copy.addAll(2, sub);
        print("17: " + copy);
        print("18: " + ints.isEmpty());
        ints.clear();
        print("19: " + ints);
        print("20: " + ints.isEmpty());
        ints.addAll(Arrays.asList("register", "vistor", "fork", "danger"));
        print("21: " + ints);
        Object[] o = ints.toArray();
        print("22: " + o[3]);
        String[] ia = ints.toArray(new String[0]);
        print("22: " + ia[3]);
    }
} /*
     * Output: 1: [1, 2, 3, 4, 5, 6, 7] 2: [1, 2, 3, 4, 5, 6, 7, 8] 3: true 4: 3
     * 2 5: 0 6: true 7: true 8: [2, 4, 5, 6, 7] 9: [2, 4, 5, 0, 6, 7] subList:
     * [4, 5, 0] 10: true sorted subList: [0, 4, 5] 11: true shuffled subList:
     * [4, 0, 5] 12: true sub: [4, 6] 13: [4, 6] 14: [2, 4, 5, 6, 7] 15: [2, 5,
     * 7] 16: [2, 9, 7] 17: [2, 9, 4, 6, 7] 18: false 19: [] 20: true 21: [1, 2,
     * 3, 4] 22: 4 22: 4 Holding Your Objects 185
     */// :~