Java之旅_高级教程_实例_数组

摘自：http://www.runoob.com/java/java-examples.html

1.数组排序及元素查找

以下实例演示了如何使用sort()方法对Java数组进行排序，及如何使用 binarySearch() 方法来查找数组中的元素, 这边我们定义了 printArray() 方法来打印数组：

package javaLearn;
import java.util.Arrays;

public class MainClass{
    public static void main(String[] args){
        int array[] = {2,5,-2,6,-3,8,0,-7,-9,4};
        Arrays.sort(array);
        printArray("数组排序结果为：",array);
        int index = Arrays.binarySearch(array, 2);
        System.out.println("元素2所在位置："+index);
        
    }
    
    private static void printArray(String message,int array[]){
        System.out.println(message+"[:length:"+array.length+"]");
        for(int i=0;i<array.length;i++){
            System.out.print(array[i]+" ");
        }
        System.out.println();
    }
}

2.数组添加元素

使用sort()方法排序，insertElement()方法向数组插入元素

package javaLearn;
import java.util.Arrays;

public class MainClass{
    public static void main(String[] args){
        int array[] ={2,5,-2,6,-3,8,0,-7,-9,4};
        Arrays.sort(array);
        printArray("数组排序：",array);
        int index = Arrays.binarySearch(array, 1);
        System.out.println("元素1所在位置(负数为不存在):"+index);
        int newindex = -index-1;
        array = insertElement(array,1,newindex);
        printArray("数组添加元素1：",array);
    }
    
    private static void printArray(String message,int array[]){
        System.out.println(message+"[:length:"+array.length+"]");
        for(int i=0;i<array.length;i++){
            System.out.print(array[i]+" ");
        }
        System.out.println();
    }
    
    private static int[] insertElement(int array[],int element,int index){
        int length = array.length;
        int destArray[] = new int[length+1];
        System.arraycopy(array, 0, destArray, 0, index);
        destArray[index] = element;
        System.arraycopy(array, index, destArray, index+1, length-index);
        return destArray;
    }
}

3.获取数组长度

public class MainClass{
    public static void main(String[] args){
        String[][] data = new String[2][5];
        System.out.println(data.length);
        System.out.println(data[0].length);
    }
}

4.数组反转

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

public class MainClass{
    public static void main(String[] args){
        ArrayList<String> arrayList = new ArrayList<String>();
        arrayList.add("A");
        arrayList.add("B");
        arrayList.add("C");
        System.out.println("排序前："+arrayList);
        Collections.reverse(arrayList);
        System.out.println("排序后："+arrayList);
    }
}

5.数组输出

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

public class MainClass{
    public static void main(String[] args){
        String[] greeting = new String[3];
        greeting[0] = "aaa";
        greeting[1] = "bbb";
        greeting[2] = "ccc";
        for(int i=0;i<greeting.length;i++){
            System.out.println(greeting[i]);
        }
        
        ArrayList<String> arrayList = new ArrayList<String>();
        arrayList.add("A");
        arrayList.add("B");
        arrayList.add("C");
        for(int i=0;i<arrayList.size();i++){
            System.out.println(arrayList.get(i));
        }
    }
}

6.数组获取最大和最小值

import java.util.*;

public class MainClass{
    public static void main(String[] args){
        Integer[] array = {8,2,7,1,4,9,5};
        List<Integer> aList =  Arrays.asList(array);//数组转换为list
        int min = Collections.min(aList);
        int max = Collections.max(aList);
        System.out.println("最小值为："+min);
        System.out.println("最大值为："+max);
    }
}

7.数组合并

import java.util.*;

public class MainClass{
    public static void main(String[] args){
        String[] a = {"A","B","C"};
        String[] b = {"D","E","F"};
        List<String> list = new ArrayList<String>(Arrays.asList(a));  //将数组a转换成list
        list.addAll(Arrays.asList(b));  //将数组b转换成list并添加到list中
        Object[] c = list.toArray();
        System.out.println(Arrays.toString(c));
    }
}

8.数组填充

import java.util.*;

public class MainClass{
    public static void main(String[] args){
        String[] a = new String[6];
        Arrays.fill(a, "aa");
        for(int i=0;i<a.length;i++){
            System.out.println(a[i]);
        }
        System.out.println("=================");
        Arrays.fill(a,3,6,"bb");
        for(int i=0;i<a.length;i++){
            System.out.println(a[i]);
        }
    }
}

 9.数组扩容

public class MainClass{
    public static void main(String[] args){
        String[] names = new String[] { "A", "B", "C" };
        String[] extended = new String[5];
        extended[3] = "D";
        extended[4] = "E";
        System.arraycopy(names, 0, extended, 0, names.length);
        for (String str : extended){
            System.out.println(str);
        }
    }
}

10.查找数组中重复元素

public class MainClass{
    public static void main(String[] args){
        int[] array = {1,2,3,4,5,2,5,6,7};
        for(int i=0;i<array.length-1;i++){
            for(int j=i+1;j<array.length;j++){
                if(array[j]==array[i]){
                    System.out.println("重复元素："+array[i]);
                }
            }
        }
    }
}

11.删除数组元素

import java.util.*;

public class MainClass{
    public static void main(String[] args){
        ArrayList<String> al = new ArrayList<String>();
        al.clear();
        al.add(0,"第一个元素");
        al.add(1,"第二个元素");
        al.add(2,"第三个元素");
        al.remove(0);
        al.remove("第三个元素");
        System.out.println(al);
    }
}

12.数组差集

import java.util.*;

    public class MainClass{
        public static void main(String[] args){
            ArrayList<String> al = new ArrayList<String>();
            ArrayList<String> al2 = new ArrayList<String>();
            al.add(0,"第一个元素");
            al.add(1,"第二个元素");
            al.add(2,"hello");
            al2.add(0,"第二个元素");
            al2.add(1,"the second");
            al2.add(2,"the third");
            al2.removeAll(al);
            System.out.println("al2与al数组差集为："+al2);
        }
    }

 13.数组交集

import java.util.*;

    public class MainClass{
        public static void main(String[] args){
            ArrayList<String> al = new ArrayList<String>();
            ArrayList<String> al2 = new ArrayList<String>();
            al.add(0,"第一个元素");
            al.add(1,"第二个元素");
            al.add(2,"hello");
            al2.add(0,"第二个元素");
            al2.add(1,"the second");
            al2.add(2,"the third");
            al2.retainAll(al);
            System.out.println("al2与al数组交集为："+al2);
        }
    }

14.在数组中查找指定元素

import java.util.*;

    public class MainClass{
        public static void main(String[] args){
            ArrayList<String> al = new ArrayList<String>();
            ArrayList<String> al2 = new ArrayList<String>();
            al.add(0,"第一个元素");
            al.add(1,"第二个元素");
            al.add(2,"hello");
            al2.add(0,"第二个元素");
            al2.add(1,"the second");
            al2.add(2,"the third");
            System.out.println("al2包含al?："+al2.contains(al));
            System.out.println("al2包含the second?"+al2.contains("the second"));
        }
    }

15.判断数组是否相等

import java.util.*;

    public class MainClass{
        public static void main(String[] args){
            int ary1[] = {1,2,3,4};
            int ary2[] = {1,2,3,4,5};
            int ary3[] = {1,2,3,4};
            System.out.println("ary1与ary2相等？："+Arrays.equals(ary1, ary2));
            System.out.println("ary1与ary3相等？："+Arrays.equals(ary1, ary3));
        }
    }

16.数组并集

import java.util.*;

    public class MainClass{
        public static void main(String[] args){
            String[] ary1 = {"1","2","3","4"};
            String[] ary2 = {"1","2","3"};
            String[] ary3 = union(ary1,ary2);
            System.out.print("并集的结果：");
            for(String str:ary3){
                System.out.print(str+" ");
            }
        }
        
        public static String[] union(String[] ary1,String[] ary2){
            Set<String> set = new HashSet<String>();//set 无序，不重复            
            for(String str:ary1){
                set.add(str);
            }
            for(String str:ary2){
                set.add(str);
            }
            String[] ary3 = {};
            return set.toArray(ary3);
        }
    }