实际应用中的 Lambda 表达式

<code class="java">interface MyValueSemLambda1 {
    double getValue();
}

class MyValueImpl implements MyValueSemLambda1 {
    private double value;

    public MyValueImpl(double value) {
        this.value = value;
    }

    @Override
    public double getValue() {
        return this.value;
    }
}

public class MyValueSemLambda {
    public static void main(String[] args) {
        MyValueSemLambda1 myVal = new MyValueImpl(98.6);
        System.out.println("Value: " + myVal.getValue()); // Prints 98.6
    }
}</code>

<code class="java">interface MyValueCompare {
    double getValue();
}

public class MyValueComparacao {
    public static void main(String[] args) {
        MyValueCompare myVal = () -> 98.6;
        System.out.println("Value: " + myVal.getValue()); // Prints 98.6
    }
}</code>

<code class="java">interface MyValue {
    double getValue();
}

interface MyParamValue {
    double getValue(double v);
}

class LambdaDemo {
    public static void main(String args[]) {
        MyValue myVal;
        myVal = () -> 98.6;
        System.out.println("Constant value: " + myVal.getValue());

        MyParamValue myPval = (n) -> 1.0 / n;
        System.out.println("Reciprocal of 4 is " + myPval.getValue(4.0));
        System.out.println("Reciprocal of 8 is " + myPval.getValue(8.0));
    }
}</code>

<code>Constant value: 98.6
Reciprocal of 4 is 0.25
Reciprocal of 8 is 0.125</code>

<code class="java">interface NumericTest {
    boolean test(int n, int m);
}

class LambdaDemo2 {
    public static void main(String args[]) {
        NumericTest isFactor = (n, d) -> (n % d) == 0;
        if (isFactor.test(10, 2))
            System.out.println("2 is a factor of 10");
        if (!isFactor.test(10, 3))
            System.out.println("3 is not a factor of 10");

        NumericTest lessThan = (n, m) -> (n < m);
        if (lessThan.test(2, 10))
            System.out.println("2 is less than 10");
        if (!lessThan.test(10, 2))
            System.out.println("10 is not less than 2");

        NumericTest absEqual = (n, m) -> (Math.abs(n) == Math.abs(m));
        if (absEqual.test(4, -4))
            System.out.println("Absolute values of 4 and -4 are equal.");
        if (!absEqual.test(4, -5))
            System.out.println("Absolute values of 4 and -5 are not equal.");
    }
}</code>

<code>2 is a factor of 10
3 is not a factor of 10
2 is less than 10
10 is not less than 2
Absolute values of 4 and -4 are equal.
Absolute values of 4 and -5 are not equal.</code>

<code class="java">interface StringTest {
    boolean test(String aStr, String bStr);
}

class LambdaDemo3 {
    public static void main(String args[]) {
        StringTest isIn = (a, b) -> a.indexOf(b) != -1;
        String str = "This is a test";
        System.out.println("Test string: " + str);
        if (isIn.test(str, "is a"))
            System.out.println("'is a' found.");
        else
            System.out.println("'is a' not found.");
        if (isIn.test(str, "xyz"))
            System.out.println("'xyz' found");
        else
            System.out.println("'xyz' not found");
    }
}</code>

<code>Test string: This is a test
'is a' found.
'xyz' not found</code>