1、带参数带返回值的方法作为入参

（1）flutter

• 定义

int add(int a, int b) => a + b;
int subtract(a, b) => a - b;performOperation(int a, int b, int Function(int, int) function) => function(a, b);// //简化写法
// add(a, b) => a + b;
// subtract(a, b) => a - b;
// performOperation(a, b, function) => function(a, b);

• 使用

void main() {var res11 = performOperation(1, 2, add);var res12 = performOperation(1, 2, (a, b) => a + b);var res21 = performOperation(1, 2, subtract);var res22 = performOperation(1, 2, (a, b) => a - b);print("res11: $res11");print("res12: $res12");print("res21: $res21");print("res22: $res22");
}

（2）kotlin

• 定义

fun add(a: Int, b: Int) = a + b
fun subtract(a: Int, b: Int) = a - bfun performOperation(a: Int, b: Int, action: (Int, Int) -> Int) = action(a, b)

• 使用

fun main() {val res11 = performOperation(1, 2, ::add)val res12 = performOperation(1, 2, action = { a: Int, b: Int -> a + b })val res21 = performOperation(1, 2, ::subtract)val res22 = performOperation(1, 2, action = { a: Int, b: Int -> a - b })println("res11: $res11")println("res12: $res12")println("res21: $res21")println("res22: $res22")
}

（3）java

• 定义

public class Test {int add(int a, int b) {return a + b;}int subtract(int a, int b) {return a - b;}int performOperation(int a, int b, BiFunction<Integer, Integer, Integer> action) {return action.apply(a, b);}}

• 使用

public class Test {int add(int a, int b) {return a + b;}int subtract(int a, int b) {return a - b;}int performOperation(int a, int b, BiFunction<Integer, Integer, Integer> action) {return action.apply(a, b);}void main(Test test) {int res11 = performOperation(1, 2, test::add);int res12 = performOperation(1, 2, (a, b) -> a + b);int res21 = performOperation(1, 2, test::subtract);int res22 = performOperation(1, 2, (a, b) -> a - b);}
}

2、带参数不带返回值的方法作为入参

（1）flutter

• 定义

equals(int a, int b, Function(bool) callback) {if (a == b) {callback(true);} else {callback(false);}
}// //简化写法
// equals(a, b, callback) {
//   if (a == b) {
//     callback(true);
//   } else {
//     callback(false);
//   }
// }

• 使用

void main() {equals(2, 5, (value) => {if (value){//相等print("res3: 相等")}else{//不相等print("res3: 不相等")}});
}

（2）kotlin

• 定义

fun equals(a: Int, b: Int, callback: (Boolean) -> Unit) {if (a == b) {callback(true)} else {callback(false)}
}

• 使用

fun main() {equals(1, 2, callback = { value ->if (value) {println("相等")} else {println("不相等")}})
}

（3）java

• 定义

public class Test {void equals(int a, int b, Function<Boolean, Void> callback) {if (a == b) {callback.apply(true);} else {callback.apply(false);}}
}

• 使用

public class Test {void equals(int a, int b, Function<Boolean, Void> callback) {if (a == b) {callback.apply(true);} else {callback.apply(false);}}void main() {equals(1, 2, (value) -> {if (value) {System.out.println("相等");} else {System.out.println("不相等");}return null;});}
}

3、不带参数不带返回值的方法作为入参

（1）flutter

checkOddNumber(int num, Function() oddCallback, Function() evenCallback) {if (num % 2 == 1) {//奇数oddCallback();} else {//偶数evenCallback();}
}// //简化写法
// checkOddNumber(num, oddCallback, evenCallback) {
//   if (num % 2 == 1) {
//     oddCallback();
//   } else {
//     evenCallback();
//   }
// }

• 使用

void main() {checkOddNumber(3, () => {print("res4: 奇数")}, () => {print("res4: 偶数")});
}

（2）kotlin

• 定义

fun checkOddNumber(num: Int, oddCallback: () -> Unit, evenCallback: () -> Unit) {if (num % 2 == 1) {oddCallback()} else {evenCallback()}
}

• 使用

fun main() {checkOddNumber(1,oddCallback = {println("奇数")},evenCallback = {println("偶数")})
}

（3）java

• 定义

public class Test {void checkOddNumber(int num, Function<Void, Void> oddCallback, Function<Void, Void> evenCallback) {if (num % 2 == 1) {oddCallback.apply(null);} else {evenCallback.apply(null);}}
}

• 使用

public class Test {void checkOddNumber(int num, Function<Void, Void> oddCallback, Function<Void, Void> evenCallback) {if (num % 2 == 1) {oddCallback.apply(null);} else {evenCallback.apply(null);}}void main() {checkOddNumber(1, (t1) -> {System.out.println("奇数");return null;}, (t2) -> {System.out.println("偶数");return null;});}
}