Array

 数组的排序：

public static void main(String[] args) {                           
    int[] arr = {11,22,44,55,33};                                  
    System.out.println(Arrays.toString(arr));//[11, 22, 44, 55, 33]
    Arrays.sort(arr);                                              
    System.out.println(Arrays.toString(arr));//[11, 22, 33, 44, 55]
}  

 数组转集合，不能增删，否则抛异常，数组的其它方法都可以。如果例子中list增加方法，例如：list.add("d") 则抛 java.lang.UnsupportedOperationException

private static void arrToList() {                     
    String[] arr = {"a","b","c"};                     
    List<String> list = Arrays.asList(arr);           
    System.out.println(list.size());                  
                                                      
    int[] ints = {1,2,3,4};                           
    List<int[]> list2 = Arrays.asList(ints);          
    System.out.println(list2.size());//长度为1           
                                                      
    //用包装类                                            
    Integer[] integers = {1,2,3,4,5,6};               
    List<Integer> list3 = Arrays.asList(integers);    
    System.out.println(list3.size());//长度为6           
} 

  合并数组：

public static String[] concat(String[] a, String[] b) {
    String[] c= new String[a.length+b.length];         
    System.arraycopy(a, 0, c, 0, a.length);            
    System.arraycopy(b, 0, c, a.length, b.length);     
    return c;                                          
}   

 数组复制

public static void main(String[] args) {                                      
    String[] strs1 = { "123", "234", "345", "456", "789" };                   
                                                                              
    String[] str2 = Arrays.copyOf(strs1, 3);                                  
    String[] str3 = Arrays.copyOf(strs1, 8);                                  
    System.out.println();                                                     
    for (String ele : str2) {                                                 
        System.out.print(ele + ";"); // 输出：123;234;345;                       
    }                                                                         
    System.out.println();                                                     
    for (String ele : str3) {                                                 
        System.out.print(ele + ";");// 输出：123;234;345;456;789;null;null;null; 
    }                                                                         
                                                                              
    int[] in = { 1, 2, 3, 4, 5 };                                             
    int[] int1 = Arrays.copyOf(in, 3);                                        
    int[] int2 = Arrays.copyOf(in, 8);                                        
                                                                              
    System.out.println();                                                     
    for (int ele : int1) {                                                    
        System.out.print(ele + ";");// 输出：1;2;3;                              
    }                                                                         
    System.out.println();                                                     
    for (int ele : int2) {                                                    
        System.out.print(ele + ";");// 输出：1;2;3;4;5;0;0;0;                    
                                                                              
    }                                                                         
                                                                              
}                                                                             

 数组相等  returns true if the arrays have equal lengths and equal elements in corresponding positions. The arrays can have component types Object, int, long, short, char, byte,boolean, float, or double.：

public static void main(String[] args) {          
    String[] str1 = {"1","2","3","4"};            
    String[] str2 = {"1","1","3","4"};            
    System.out.println(Arrays.equals(str1, str2));
}                                                 

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