Justin's Words

Java Collections

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惯例，先上代码：

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package co.young.DataStructure;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionsExample {
    public static void main(String[] args) {
        List<Double> temperatureList = new ArrayList<Double>();

        temperatureList.add(40.5);
        temperatureList.add(33.9);
        temperatureList.add(37.8);
        temperatureList.add(15.3);
        temperatureList.add(25.6);

        // Print elements of temperatureList
        System.out.println(temperatureList);

        // Sorting List in ascending order according to the natural ordering
        Collections.sort(temperatureList);
        System.out.println("Sorted List: "+temperatureList);

        // Searching a temperature from list
        int searchIndex = Collections.binarySearch(temperatureList, 37.8);
        if(searchIndex >=0){
            System.out.println("Temperature found at " + searchIndex + ".");
        } else{
            System.out.println("Temperature not found.");
        }

        //Shuffles the list
        Collections.shuffle(temperatureList);
        System.out.println("Shuffled List: "+temperatureList);

        //Get maximum temperature from temperatureList
        Double max = Collections.max(temperatureList);
        System.out.println("Maximun temperature: "+max);

        //Get minimum temperature from temperatureList
        Double min = Collections.min(temperatureList);
        System.out.println("Minimum temperature: "+min);

        //Reverse the list
        Collections.reverse(temperatureList);
        System.out.println("Reversed List: "+temperatureList);

        //Copy elements from one list to another
        List<Double> newTemperatureList = new ArrayList<Double>(temperatureList.size());
        newTemperatureList.add(13.6);
        newTemperatureList.add(10.2);
        newTemperatureList.add(42.9);
        newTemperatureList.add(34.4);
        newTemperatureList.add(27.2);
        System.out.println("New temperature list: "+newTemperatureList);
        Collections.copy(newTemperatureList, temperatureList);
        System.out.println("New temperature list after copy: "+newTemperatureList);

        //Replaces all occurrences of one specified value in a list with another.
        Collections.replaceAll(temperatureList, 40.5, 0.0);
        System.out.println("After replaceAll: "+temperatureList);

        //Fill temperatureList.
        Collections.fill(temperatureList, 0.0);
        System.out.println("Filled List: "+temperatureList);
    }
}

方法分析

跳去关于 ArrayList 的博文。

按升序排序列表

格式：

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static <T> void sort(List<T> list, Comparator<? super T> c);

使用：

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Collections.sort(temperatureList);

查找指定元素所在的位置

格式：

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static <T> int binarySearch(List<? extend Comparable<? super T>> list, T key);

使用：

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int searchIndex = Collections.binarySearch(temperatureList, 37.8);
if(searchIndex >=0){
    System.out.println("Temperature found at " + searchIndex + ".");
} else{
    System.out.println("Temperature not found.");
}

打乱列表元素顺序

shuffle，洗牌。

格式：

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static void shuffle(List<?> list);

使用：

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int searchIndex = Collections.binarySearch(temperatureList, 37.8);
if(searchIndex >=0){
    System.out.println("Temperature found at " + searchIndex + ".");
} else{
    System.out.println("Temperature not found.");
}

获取列表最大值和获取列表最小值

格式：

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static <T extends Object & Comparable<? super T>> max(Collection<? extends T> coll);
static <T extends Object & Comparable<? super T>> min(Collection<? extends T> coll)

使用：

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//Get maximum temperature from temperatureList
Double max = Collections.max(temperatureList);
System.out.println("Maximun temperature: "+max);

//Get minimum temperature from temperatureList
Double min = Collections.min(temperatureList);
System.out.println("Minimum temperature: "+min);

倒转列表元素排序

格式：

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static void reverse(List<?> list);

使用：

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//Reverse the list
Collections.reverse(temperatureList);
System.out.println("Reversed List: "+temperatureList);

复制列表

格式：

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public static <T> void copy(List<? super T> dest, List<? extends T> src);

使用：

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//Copy elements from one list to another
List<Double> newTemperatureList = new ArrayList<Double>(temperatureList.size());
newTemperatureList.add(13.6);
newTemperatureList.add(10.2);
newTemperatureList.add(42.9);
newTemperatureList.add(34.4);
newTemperatureList.add(27.2);
System.out.println("New temperature list: "+newTemperatureList);
Collections.copy(newTemperatureList, temperatureList);
System.out.println("New temperature list after copy: "+newTemperatureList);

输出：

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New temperature list: [13.6, 10.2, 42.9, 34.4, 27.2]
New temperature list after copy: [25.6, 33.9, 40.5, 15.3, 37.8]

替换指定元素

格式：

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public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal);

使用：

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//Replaces all occurrences of one specified value in a list with another.
Collections.replaceAll(temperatureList, 40.5, 0.0);
System.out.println("After replaceAll: "+temperatureList);

输出：

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After replaceAll: [25.6, 33.9, 0.0, 15.3, 37.8]

给列表充满指定元素

格式：

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public static <T> void fill(List<? super T> list, T obj)

使用：

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//Fill temperatureList.
Collections.fill(temperatureList, 0.0);
System.out.println("Filled List: "+temperatureList);

输出：

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Filled List: [0.0, 0.0, 0.0, 0.0, 0.0]