Java中containsKey 、 contains 方法详解及代码举例详解

boolean containsKey(Object key)

import java.util.HashMap;
import java.util.Map;
public class ContainsKeyExample {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("apple", 10);
        map.put("banana", 20);
        System.out.println(map.containsKey("apple"));  // true
        System.out.println(map.containsKey("orange")); // false
    }
}

boolean contains(Object o)

import java.util.ArrayList;
import java.util.List;
public class ContainsExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("apple");
        list.add("banana");
        System.out.println(list.contains("apple"));  // true
        System.out.println(list.contains("orange")); // false
    }
}

boolean contains(CharSequence sequence)

public class StringContainsExample {
    public static void main(String[] args) {
        String str = "Hello, world!";
        System.out.println(str.contains("world"));  // true
        System.out.println(str.contains("Java"));   // false
    }
}

import java.util.*;
public class CombinedExample {
    public static void main(String[] args) {
        Map<String, List<String>> map = new HashMap<>();
        List<String> fruits = new ArrayList<>();
        fruits.add("apple");
        fruits.add("banana");
        map.put("fruits", fruits);
        System.out.println(map.containsKey("fruits"));      // true
        System.out.println(fruits.contains("apple"));       // true
        System.out.println("banana".contains("ana"));       // true
    }
}