November 21, 2019 Java Learning

String buffer, improve the efficiency of string usage
Common usage of StringBuilder
public static void append(): add any type of data in the form of a string, and return the current object itself


1. The difference between array and collection:
1. The length of the array is fixed Yes, the length of the collection can be changed
2. The array stores elements of the same type, which can store basic data type values; while the collection stores all objects, and the types of objects can be different. There are many objects in development At times, use collections for storage.
2. Define a method containing generics:
format:
modifier <generic> return value type method name (parameter list (using generics)) { method body} 3. Wildcard for generics ? Cannot be used when defining, but can be used when passing as a parameter . Advanced use of wildcards: 1. The upper limit of generics:? extends E—>? Can only be a subclass of E or E itself 2, the upper limit of generics:? super E---->? can only be the parent of E or E itself