检查Java中的数组中是否存在值

给定一个数组，任务是编写一个Java程序来检查该数组中是否存在特定元素。

例子：

Input: arr[] = [5, 1, 1, 9, 7, 2, 6, 10], key = 7
Output: true

Input: arr[] = [-1, 1, 5, 8], key = -2
Output: false

数组是包含一组元素的数据结构。通常，这些元素都是相同的数据类型，例如整数或字符串。数组通常在计算机程序中用于组织数据，以便可以快速排序或搜索相关的一组值。数组的所有项目都存储在连续的内存位置。

方法

有许多方法可以检查此 Array 中是否存在特定Java。这些都是 -

• 使用线性搜索方法
• 使用二分搜索方法
• 使用 List.contains() 方法
• 使用 Stream.anyMatch() 方法

1.使用线性搜索方法：

在这种情况下，列表或数组按顺序遍历，并检查每个元素。

句法：

for (int element : arr) {
    if (element == toCheckValue) {
        return true;
    }
}

例子：

Java

// Java program to check whether
// an element is present in array or not
 
import java.util.Arrays;
import java.util.stream.IntStream;
 
class GFG {
 
    // Function return true if given element
    // found in array
    private static void check(int[] arr, int toCheckValue)
    {
        // check if the specified element
        // is present in the array or not
        // using Linear Search method
        boolean test = false;
        for (int element : arr) {
            if (element == toCheckValue) {
                test = true;
                break;
            }
        }
 
        // Print the result
        System.out.println("Is " + toCheckValue
                           + " present in the array: " + test);
    }
 
    public static void main(String[] args)
    {
 
        // Get the array
        int arr[] = { 5, 1, 1, 9, 7, 2, 6, 10 };
 
        // Get the value to be checked
        int toCheckValue = 7;
 
        // Print the array
        System.out.println("Array: "
                           + Arrays.toString(arr));
 
        // Check if this value is
        // present in the array or not
        check(arr, toCheckValue);
    }
}

输出

Array: [5, 1, 1, 9, 7, 2, 6, 10]
Is 7 present in the array: true

2.使用二分查找法：

在这种情况下，通过重复将搜索间隔分成两半来搜索排序数组。从覆盖整个数组的间隔开始。如果搜索键的值小于区间中间的项，则将区间缩小到下半部分。否则，将其缩小到上半部分。反复检查，直到找到值或区间为空。
在此示例中，Arrays.binarySearch() 方法用于二进制搜索。

句法：

public static int 
    binarySearch(data_type arr, data_type key)

例子：

Java

// Java program to check whether
// an element is present in array or not
 
import java.util.Arrays;
import java.util.stream.IntStream;
 
class GFG {
 
    // Function return true if given element
    // found in array
    private static void check(int[] arr, int toCheckValue)
    {
        // sort given array
        Arrays.sort(arr);
 
        // check if the specified element
        // is present in the array or not
        // using Binary Search method
        int res = Arrays.binarySearch(arr, toCheckValue);
 
        boolean test = res > 0 ? true : false;
 
        // Print the result
        System.out.println("Is " + toCheckValue
                           + " present in the array: " + test);
    }
 
    public static void main(String[] args)
    {
 
        // Get the array
        int arr[] = { 5, 1, 1, 9, 7, 2, 6, 10 };
 
        // Get the value to be checked
        int toCheckValue = 7;
 
        // Print the array
        System.out.println("Array: "
                           + Arrays.toString(arr));
 
        // Check if this value is
        // present in the array or not
        check(arr, toCheckValue);
    }
}

输出

Array: [5, 1, 1, 9, 7, 2, 6, 10]
Is 7 present in the array: true

3. 使用List.contains()方法：

Java中的 List contains() 方法用于检查指定元素是否存在于给定列表中。

句法：

public boolean contains(Object)

要搜索的对象元素在哪里。

例子：

Java

// Java program to check whether
// an element is present in array or not
 
import java.util.Arrays;
 
class GFG {
 
    // Function return true if given element
    // found in array
    private static void check(Integer[] arr, int toCheckValue)
    {
        // check if the specified element
        // is present in the array or not
        // using contains() method
        boolean test
            = Arrays.asList(arr)
                  .contains(toCheckValue);
 
        // Print the result
        System.out.println("Is " + toCheckValue
                           + " present in the array: " + test);
    }
 
    public static void main(String[] args)
    {
 
        // Get the array
        Integer arr[] = { 5, 1, 1, 9, 7, 2, 6, 10 };
 
        // Get the value to be checked
        int toCheckValue = 7;
 
        // Print the array
        System.out.println("Array: "
                           + Arrays.toString(arr));
 
        // Check if this value is
        // present in the array or not
        check(arr, toCheckValue);
    }
}

输出

Array: [5, 1, 1, 9, 7, 2, 6, 10]
Is 7 present in the array: true

4. 使用Stream.anyMatch()方法：

Stream anyMatch(Predicate predicate) 返回此流的任何元素是否与提供的谓词匹配。如果不需要确定结果，它可能不会评估所有元素的谓词。

句法：

boolean anyMatch(Predicate predicate)

Where T is the type of the input to the predicate
and the function returns true if any elements of
the stream match the provided predicate, 
otherwise false.

示例 1：使用 Stream.of() 方法创建 Stream

Java

// Java program to check whether
// an element is present in array or not
 
import java.util.Arrays;
import java.util.stream.IntStream;
 
class GFG {
 
    // Function return true if given element
    // found in array
    private static void check(int[] arr, int toCheckValue)
    {
        // check if the specified element
        // is present in the array or not
        // using anyMatch() method
        boolean test
            = IntStream.of(arr)
                  .anyMatch(x -> x == toCheckValue);
 
        // Print the result
        System.out.println("Is " + toCheckValue
                           + " present in the array: " + test);
    }
 
    public static void main(String[] args)
    {
 
        // Get the array
        int arr[] = { 5, 1, 1, 9, 7, 2, 6, 10 };
 
        // Get the value to be checked
        int toCheckValue = 7;
 
        // Print the array
        System.out.println("Array: "
                           + Arrays.toString(arr));
 
        // Check if this value is
        // present in the array or not
        check(arr, toCheckValue);
    }
}

输出

Array: [5, 1, 1, 9, 7, 2, 6, 10]
Is 7 present in the array: true

示例 2：使用 Arrays.stream() 方法创建 Stream

Java

// Java program to check whether
// an element is present in array or not
 
import java.util.Arrays;
import java.util.stream.IntStream;
 
class GFG {
 
    // Function return true if given element
    // found in array
    private static void check(int[] arr, int toCheckValue)
    {
        // check if the specified element
        // is present in the array or not
        // using anyMatch() method
        boolean test
            = IntStream.of(arr)
                  .anyMatch(x -> x == toCheckValue);
 
        // Print the result
        System.out.println("Is " + toCheckValue
                           + " present in the array: " + test);
    }
 
    public static void main(String[] args)
    {
 
        // Get the array
        int arr[] = { 5, 1, 1, 9, 7, 2, 6, 10 };
 
        // Get the value to be checked
        int toCheckValue = 7;
 
        // Print the array
        System.out.println("Array: "
                           + Arrays.toString(arr));
 
        // Check if this value is
        // present in the array or not
        check(arr, toCheckValue);
    }
}

输出

Array: [5, 1, 1, 9, 7, 2, 6, 10]
Is 7 present in the array: true