Java中的集合 max() 方法和示例

最大（集合<？扩展 T> coll）

Java.util.Collections类的max()方法用于根据元素的自然顺序返回给定集合的最大元素。集合中的所有元素都必须实现 Comparable 接口。此外，集合中的所有元素必须相互可比较（即，e1.compareTo(e2) 不得为集合中的任何元素 e1 和 e2 抛出 ClassCastException）。
此方法迭代整个集合，因此它需要与集合大小成正比的时间。

句法：

public static  T
  max(Collection coll)

参数：该方法将collection coll作为参数来确定其最大元素。
返回值：此方法根据元素的自然顺序返回给定集合的最大元素。

异常：此方法抛出以下异常：

• ClassCastException –如果集合包含不可相互比较的元素（例如，字符串和整数）。
• NoSuchElementException –如果集合为空

以下是说明max()方法的示例

示例 1：

Java

// Java program to demonstrate
// max() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of LinkedList
            List list = new LinkedList();
 
            // Adding element to Vector v
            list.add(-1);
            list.add(4);
            list.add(-5);
            list.add(1);
 
            // printing the max value
            // using max() method
            System.out.println("Max value is: "
                               + Collections.max(list));
        }
 
        catch (ClassCastException e) {
            System.out.println("Exception thrown : " + e);
        }
 
        catch (NoSuchElementException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Max value is: 4

示例 2：对于ClassCastException

Java

// Java program to demonstrate
// max() method for ClassCastException
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of LinkedList
            List list = new LinkedList();
 
            // creating variable of object type
            Object i = Integer.valueOf(42);
 
            // Adding element to Vector v
            list.add("Hello");
            list.add((String)i);
 
            // printing the max value
            // using max() method
            System.out.println("Max value is: "
                               + Collections.max(list));
        }
 
        catch (ClassCastException e) {
            System.out.println("Exception thrown : " + e);
        }
 
        catch (NoSuchElementException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Exception thrown : java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

示例 3：对于NoSuchElementException

Java

// Java program to demonstrate
// max() method for NoSuchElementException
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of LinkedList
            List list = new LinkedList();
 
            // printing the max value
            // using max() method
            System.out.println("Trying to get "
                               + "the max from empty list");
            System.out.println("Max value is: "
                               + Collections.max(list));
        }
 
        catch (ClassCastException e) {
            System.out.println("Exception thrown : " + e);
        }
 
        catch (NoSuchElementException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Trying to get the max from empty list
Exception thrown : java.util.NoSuchElementException

公共静态 T max(Collection coll, Comparator comp)

Java.util.Collections类的max()方法用于根据指定比较器诱导的顺序返回给定集合的最大元素。集合中的所有元素必须通过指定的比较器相互比较（即，comp.compare(e1, e2) 不得为集合中的任何元素 e1 和 e2 抛出 ClassCastException）。
此方法迭代整个集合，因此它需要与集合大小成正比的时间。

参数：此方法将以下参数作为参数

• coll -要确定其最大元素的集合。
• comp –用于确定最大元素的比较器。空值表示应使用元素的自然顺序。

返回值：此方法根据指定的比较器返回给定集合的最大元素。

异常：此方法抛出以下异常：

• ClassCastException –如果集合包含不可相互比较的元素（例如，字符串和整数）。
• NoSuchElementException –如果集合为空

以下是说明max()方法的示例

示例 1：

Java

// Java program to demonstrate
// max() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of LinkedList
            List list = new LinkedList();
 
            // Adding element to Vector v
            list.add(-1);
            list.add(4);
            list.add(-5);
            list.add(1);
 
            // printing the max value
            // using max() method
            System.out.println("Max val: "
                               + Collections.max(list,
                                                 Collections.reverseOrder()));
        }
 
        catch (ClassCastException e) {
            System.out.println("Exception thrown : " + e);
        }
 
        catch (NoSuchElementException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Max val: -5

示例 2：对于ClassCastException

Java

// Java program to demonstrate
// max() method for ClassCastException
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of LinkedList
            List list = new LinkedList();
 
            // creating variable of object type
            Object i = Integer.valueOf(42);
 
            // Adding element to Vector v
            list.add("Hello");
            list.add((String)i);
 
            // printing the max value
            // using max() method
            System.out.println("Max val: "
                               + Collections
                                     .max(list,
                                          Collections
                                              .reverseOrder()));
        }
 
        catch (ClassCastException e) {
            System.out.println("Exception thrown : " + e);
        }
 
        catch (NoSuchElementException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Exception thrown : java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

示例 3：对于NoSuchElementException

Java

// Java program to demonstrate
// max() method for NoSuchElementException
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of LinkedList
            List list = new LinkedList();
 
            // printing the max value
            // using max() method
            System.out.println("Trying to get "
                               + "the max from empty list");
            System.out.println("Max val: "
                               + Collections
                                     .max(list,
                                          Collections
                                              .reverseOrder()));
        }
 
        catch (ClassCastException e) {
            System.out.println("Exception thrown : " + e);
        }
 
        catch (NoSuchElementException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Trying to get the max from empty list
Exception thrown : java.util.NoSuchElementException