Basic Java Knowledge

First, the data type

1.java, all numeric types account for the number of bytes and platform-independent, there is no unsigned type in Java

2. For overflow floating-point type, expressed in Nan. Double.isnan (x)

3.char type accounted for 2 bytes

4. Boolean types cannot be converted to integers, avoiding the IF (x=3) problem in C + +, if the conversion is possible. ：

5.&& | | Will short circuit

6. Two operands if one is a double, the other is converted to double

If one is float, the other will turn into a float

If one is long, the other is converted to long;

Second, string

A 1.java string is a sequence of Unicode characters.

2.1 A String class object is an immutable string that can be modified to refer to another string.

Pros: The compiler can let strings be shared, with various strings in the common storage pool. Only string constants are shared, and the results of operations such as + or substring are not shared;

equals compares content, and = = Compares location only

2.2 Common APIs:

CharAt (), CompareTo () Endwith () equals () Equalsignorecase () indexOf ()

LastIndexOf () Length () Replace () substring () toLowerCase () toUpperCase () trim ()

3. Building a String

StringBuilder high efficiency, suitable for single thread

StringBuffer low efficiency, suitable for multi-threaded

4.Scanner

Scanner (InputStream in) Scanner (new File ()) Scanner (String str)

Nextline () line next () Word Nextint () nextdouble () Hasnext ()

PrintWriter (file f) constructs a printwriter that writes to a file

Four, array

1.array.copyof (oldarray,length) is often used for expansion, and arrays are allocated on the heap.

2.array.tostring (type[] a)

3.array.sort () BinarySearch () Fill ()

Basic Java Knowledge