java学习之旅62--数组的拷贝_排序_二分法_命令行参数_增强for循环

本文链接：https://blog.youkuaiyun.com/southeast_px/article/details/46930657

本文深入讲解了Java中数组的常用操作，包括数组拷贝、排序、二分查找、填充及转换为List的方法，并通过示例代码展示具体实现过程。

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数组常见操作

数组的拷贝
- System类里包含了一个 public static void arraycopy(Object src, int srcPos,Object dest, int destPos, int length)方法，该方法可以将src数组里的元素赋给dest数组的元素，其中srcPos指定从src数组的第几个元素开始赋值，length参数指定将src数组的多少个元素赋给dest数组的元素
- 补充：打印数组 Arrays.toString(arr)
- ```
public class TestArrayCopy {
```
- ```
<pre name="code" class="java" style="font-size: 18px; font-weight: bold;">	public static void main(String[] args) {
		int[] srcArr = new int[]{2,5,3,8,9,7};
		int[] destArr = new int[5];
		System.arraycopy(srcArr, 1, destArr, 1, 3);
		System.out.println(Arrays.toString(destArr));//[0, 5, 3, 8, 0]
	}
}
```

数组的排序

Arrays.sort(arr)

public class TestArraySort {
	public static void main(String[] args) {
	     int[] arr = {23,3,67,44,66,89,12};
	     System.out.println(Arrays.toString(arr));//[23, 3, 67, 44, 66, 89, 12]
	     Arrays.sort(arr);
	     System.out.println(Arrays.toString(arr));//[3, 12, 23, 44, 66, 67, 89]
		
	}
}

如果数组中的元素是引用类型，怎么排序？

Man.java
public class Man implements Comparable<Man> {
	private int id;
	private int age;
	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}
	
	public Man() {
	}
	public Man(int id, int age) {
		super();
		this.id = id;
		this.age = age;
	}

	@Override
	public String toString() {
		return "Man [id=" + id + ", age=" + age + "]";
	}

	@Override
	public int compareTo(Man man) {
		if(this.age < man.age){
			return -1;
		}
		if(this.age > man.age){
			return 1;
		}
		return 0;
	}
	
}

<pre name="code" class="java" style="font-size: 18px; font-weight: bold;"><pre name="code" class="java">TestArraySort.java
public class TestArraySort {
	public static void main(String[] args) {
		Man[] mans = new Man[]{new Man(1, 30),new Man(1, 23),new Man(1, 60),new Man(1, 55)};
		System.out.println(Arrays.toString(mans));//[Man [id=1, age=30], Man [id=1, age=23], Man [id=1, age=60], Man [id=1, age=55]]
		Arrays.sort(mans);
		System.out.println(Arrays.toString(mans));//[Man [id=1, age=23], Man [id=1, age=30], Man [id=1, age=55], Man [id=1, age=60]]
		
	}
}

数组的二分查找

Arrays.binarySearch(arr)

public class TestBinarySearch {
	public static void main(String[] args) {
	    int[] arr = {12,3,34,21,45,3,32};
	    Arrays.sort(arr);
	    System.out.println(Arrays.toString(arr));//[3, 3, 12, 21, 32, 34, 45]
            System.out.println(Arrays.binarySearch(arr, 21));//3
	}
}

数组的填充

Arrays.fill(arr)

public class TestArrayFill {
	public static void main(String[] args) {
	    int[] arr = {12,3,34,21,45,3,32};
	    System.out.println(Arrays.toString(arr));//[12, 3, 34, 21, 45, 3, 32]
	    Arrays.fill(arr,2,4,99);
	    System.out.println(Arrays.toString(arr));//[12, 3, 99, 99, 45, 3, 32]
	}
}

数组转换为List

Arrays.asList(arr)

public class TestArrayAsList {
	public static void main(String[] args) {
		int[] arr = {12,3,34,21,45,3,32};
		List<int[]> list = new ArrayList<int[]>();
		list = Arrays.asList(arr);
		System.out.println(list.get(0)[3]);//21
	}
}

冒泡排序

public class TestBubbleSort {
	public static void main(String[] args) {
		int[] arr = {12,3,34,21,45,3,32};
		bubbleSort(arr);
		System.out.println(Arrays.toString(arr));
	}

	public  static void bubbleSort(int[] arr) {
		int temp;
		for(int i=0;i<arr.length-1;i++){
			for(int j=0;j<arr.length-1-i;j++){
				if(arr[j]>arr[j+1]){
					temp = arr[j];
					arr[j] = arr[j+1];
					arr[j+1] = temp; 
				}
			}
		}
	}
}

命令行参数