## [運算符總結](https://lingcoder.gitee.io/onjava8/#/book/04-Operators?id=%e8%bf%90%e7%ae%97%e7%ac%a6%e6%80%bb%e7%bb%93) 上述示例分別向我們展示了哪些基本類型能被用于特定的運算符。基本上，下面的代碼示例是對上述所有示例的重復，只不過概括了所有的基本類型。這個文件能被正確地編譯，因為我已經把編譯不通過的那部分用注釋`//`過濾了。代碼示例： ~~~ // operators/AllOps.java // 測試所有基本類型的運算符操作 // 看看哪些是能被 Java 編譯器接受的 public class AllOps { // 布爾值的接收測試： void f(boolean b) {} void boolTest(boolean x, boolean y) { // 算數運算符： //- x = x * y; //- x = x / y; //- x = x % y; //- x = x + y; //- x = x - y; //- x++; //- x--; //- x = +y; //- x = -y; // 關系運算符和邏輯運算符： //- f(x > y); //- f(x >= y); //- f(x < y); //- f(x <= y); f(x == y); f(x != y); f(!y); x = x && y; x = x || y; // 按位運算符： //- x = ~y; x = x & y; x = x | y; x = x ^ y; //- x = x << 1; //- x = x >> 1; //- x = x >>> 1; // 聯合賦值： //- x += y; //- x -= y; //- x *= y; //- x /= y; //- x %= y; //- x <<= 1; //- x >>= 1; //- x >>>= 1; x &= y; x ^= y; x |= y; // 類型轉換： //- char c = (char)x; //- byte b = (byte)x; //- short s = (short)x; //- int i = (int)x; //- long l = (long)x; //- float f = (float)x; //- double d = (double)x; } void charTest(char x, char y) { // 算數運算符： x = (char)(x * y); x = (char)(x / y); x = (char)(x % y); x = (char)(x + y); x = (char)(x - y); x++; x--; x = (char) + y; x = (char) - y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); // 按位運算符： x= (char)~y; x = (char)(x & y); x = (char)(x | y); x = (char)(x ^ y); x = (char)(x << 1); x = (char)(x >> 1); x = (char)(x >>> 1); // 聯合賦值： x += y; x -= y; x *= y; x /= y; x %= y; x <<= 1; x >>= 1; x >>>= 1; x &= y; x ^= y; x |= y; // 類型轉換 //- boolean bl = (boolean)x; byte b = (byte)x; short s = (short)x; int i = (int)x; long l = (long)x; float f = (float)x; double d = (double)x; } void byteTest(byte x, byte y) { // 算數運算符： x = (byte)(x* y); x = (byte)(x / y); x = (byte)(x % y); x = (byte)(x + y); x = (byte)(x - y); x++; x--; x = (byte) + y; x = (byte) - y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); //按位運算符： x = (byte)~y; x = (byte)(x & y); x = (byte)(x | y); x = (byte)(x ^ y); x = (byte)(x << 1); x = (byte)(x >> 1); x = (byte)(x >>> 1); // 聯合賦值： x += y; x -= y; x *= y; x /= y; x %= y; x <<= 1; x >>= 1; x >>>= 1; x &= y; x ^= y; x |= y; // 類型轉換： //- boolean bl = (boolean)x; char c = (char)x; short s = (short)x; int i = (int)x; long l = (long)x; float f = (float)x; double d = (double)x; } void shortTest(short x, short y) { // 算術運算符： x = (short)(x * y); x = (short)(x / y); x = (short)(x % y); x = (short)(x + y); x = (short)(x - y); x++; x--; x = (short) + y; x = (short) - y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); // 按位運算符： x = (short) ~ y; x = (short)(x & y); x = (short)(x | y); x = (short)(x ^ y); x = (short)(x << 1); x = (short)(x >> 1); x = (short)(x >>> 1); // Compound assignment: x += y; x -= y; x *= y; x /= y; x %= y; x <<= 1; x >>= 1; x >>>= 1; x &= y; x ^= y; x |= y; // 類型轉換： //- boolean bl = (boolean)x; char c = (char)x; byte b = (byte)x; int i = (int)x; long l = (long)x; float f = (float)x; double d = (double)x; } void intTest(int x, int y) { // 算術運算符： x = x * y; x = x / y; x = x % y; x = x + y; x = x - y; x++; x--; x = +y; x = -y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); // 按位運算符： x = ~y; x = x & y; x = x | y; x = x ^ y; x = x << 1; x = x >> 1; x = x >>> 1; // 聯合賦值： x += y; x -= y; x *= y; x /= y; x %= y; x <<= 1; x >>= 1; x >>>= 1; x &= y; x ^= y; x |= y; // 類型轉換： //- boolean bl = (boolean)x; char c = (char)x; byte b = (byte)x; short s = (short)x; long l = (long)x; float f = (float)x; double d = (double)x; } void longTest(long x, long y) { // 算數運算符： x = x * y; x = x / y; x = x % y; x = x + y; x = x - y; x++; x--; x = +y; x = -y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); // 按位運算符： x = ~y; x = x & y; x = x | y; x = x ^ y; x = x << 1; x = x >> 1; x = x >>> 1; // 聯合賦值： x += y; x -= y; x *= y; x /= y; x %= y; x <<= 1; x >>= 1; x >>>= 1; x &= y; x ^= y; x |= y; // 類型轉換： //- boolean bl = (boolean)x; char c = (char)x; byte b = (byte)x; short s = (short)x; int i = (int)x; float f = (float)x; double d = (double)x; } void floatTest(float x, float y) { // 算數運算符： x = x * y; x = x / y; x = x % y; x = x + y; x = x - y; x++; x--; x = +y; x = -y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); // 按位運算符： //- x = ~y; //- x = x & y; //- x = x | y; //- x = x ^ y; //- x = x << 1; //- x = x >> 1; //- x = x >>> 1; // 聯合賦值： x += y; x -= y; x *= y; x /= y; x %= y; //- x <<= 1; //- x >>= 1; //- x >>>= 1; //- x &= y; //- x ^= y; //- x |= y; // 類型轉換： //- boolean bl = (boolean)x; char c = (char)x; byte b = (byte)x; short s = (short)x; int i = (int)x; long l = (long)x; double d = (double)x; } void doubleTest(double x, double y) { // 算術運算符： x = x * y; x = x / y; x = x % y; x = x + y; x = x - y; x++; x--; x = +y; x = -y; // 關系和邏輯運算符： f(x > y); f(x >= y); f(x < y); f(x <= y); f(x == y); f(x != y); //- f(!x); //- f(x && y); //- f(x || y); // 按位運算符： //- x = ~y; //- x = x & y; //- x = x | y; //- x = x ^ y; //- x = x << 1; //- x = x >> 1; //- x = x >>> 1; // 聯合賦值： x += y; x -= y; x *= y; x /= y; x %= y; //- x <<= 1; //- x >>= 1; //- x >>>= 1; //- x &= y; //- x ^= y; //- x |= y; // 類型轉換： //- boolean bl = (boolean)x; char c = (char)x; byte b = (byte)x; short s = (short)x; int i = (int)x; long l = (long)x; float f = (float)x; } } ~~~ **注意**：**boolean**類型的運算是受限的。你能為其賦值`true`或`false`，也可測試它的值是否是`true`或`false`。但你不能對其作加減等其他運算。 在**char**，**byte**和**short**類型中，我們可以看到算術運算符的“類型轉換”效果。我們必須要顯式強制類型轉換才能將結果重新賦值為原始類型。對于**int**類型的運算則不用轉換，因為默認就是**int**型。雖然我們不用再停下來思考這一切是否安全，但是兩個大的 int 型整數相乘時，結果有可能超出**int**型的范圍，這種情況下結果會發生溢出。下面的代碼示例： ~~~ // operators/Overflow.java // 厲害了！內存溢出 public class Overflow { public static void main(String[] args) { int big = Integer.MAX_VALUE; System.out.println("big = " + big); int bigger = big * 4; System.out.println("bigger = " + bigger); } } ~~~ 輸出結果： ~~~ big = 2147483647 bigger = -4 ~~~ 編譯器沒有報錯或警告，運行時一切看起來都無異常。誠然，Java 是優秀的，但是還不足夠優秀。 對于**char**，**byte**或者**short**，混合賦值并不需要類型轉換。即使為它們執行轉型操作，也會獲得與直接算術運算相同的結果。另外，省略類型轉換可以使代碼顯得更加簡練。總之，除**boolean**以外，其他任何兩種基本類型間都可進行類型轉換。當我們進行向下轉換類型時，需要注意結果的范圍是否溢出，否則我們就很可能在不知不覺中丟失精度。