Bit operation marks multiple switches with one parameter

For example, a mobile phone , There may be the following flag bits ：

flag = Mobile phone properties

• Whether the screen is damaged case1
• Whether the battery is charged case2
• Is there a camera case3
• Can I make a phone call case4
• Whether it's an Apple phone case5
• Whether it is within the warranty period case6

Normal people may use bool Type to store n Multiple parameters , But you can also use a int Or is it long To store , stay java in int Occupy 4 Bytes each byte accounts for 8 A total of 32 position , That is to say, it can store 32 The marks are , save 32 individual bool value .

Use bit operations to operate on a int Tag for value ,int The size of the value itself makes no sense , Only focus on the binary corresponding position ,0 For unmarked ,1 Means marked .

to flag Add tag

The formula ：

flag |= case1
flag |= case2
flag |= case2|case2

Binary computing Demo ：

flag            = 0000 0000
case1           = 0000 0001
case2           = 0000 0100
 Or after operation ↓
flag            = 0000 0101

Judgment marks

The formula ：

// Single mark judgment 
bool = (flag & case1) != 0
// Composite mark judgment 
bool = (flag & control) != 0

Binary computing Demo ：

flag            = 0000 0000
case1           = 0000 0001
 And after the operation ↓
flag            = 0000 0000

Delete tag

The formula ：

flag &= ~case1

Binary computing Demo ：

case1           = 0000 0001
~case1          = 1111 1110
flag            = 0000 0001
flag&=~case1    = 0000 0000

Tips

Single meaning case No similar 0010 0001, Two marker bits appear , Unless it's a composite case, in addition case The positions between them cannot conflict .

java Can be defined by shift method case：

int flag = 0;       // 0000 0000 0000 0000 0000 0000 0000 0000
int case1 = 1;      // 0000 0000 0000 0000 0000 0000 0000 0001
int case2 = 1 << 1; // 0000 0000 0000 0000 0000 0000 0000 0010
int case3 = 1 << 2; // 0000 0000 0000 0000 0000 0000 0000 0100
int case4 = 1 << 3; // 0000 0000 0000 0000 0000 0000 0000 1000

Sample code

int flag  = 0 << 0;
int case1 = 1 << 0;
int case2 = 1 << 1;
int case3 = 1 << 2;
int case4 = 1 << 31;
// To mark 
flag |= case1;
flag |= case2;
flag |= case3;
flag |= case4;
// Verification mark 
Assert.assertTrue((flag & case1) != 0);
Assert.assertTrue((flag & case2) != 0);
Assert.assertTrue((flag & case3) != 0);
Assert.assertTrue((flag & case4) != 0);
// Delete tag 
flag &= ~case1;
flag &= ~case2;
flag &= ~case3;
flag &= ~case4;
// Verification mark 
Assert.assertFalse((flag & case1) != 0);
Assert.assertFalse((flag & case2) != 0);
Assert.assertFalse((flag & case3) != 0);
Assert.assertFalse((flag & case4) != 0);