guava Preconditions

1.checkArgument

2.checkState

3.checkNotNull

4.checkElementIndex

5.checkPositionIndex

该类就这五种重载方法。

1. checkArgument   用作检查参数

1.1 单纯的判断表达式
public static void checkArgument(boolean expression) {
        if (!expression) {
            throw new IllegalArgumentException();
        }
}

1.2  规定表达式false 返回的错误信息
public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
        if (!expression) {
            throw new IllegalArgumentException(String.valueOf(errorMessage));
        }
}
1.3 表达式， 错误模板， 错误信息
public static void checkArgument(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) {
        if (!expression) {
            throw new IllegalArgumentException(Strings.lenientFormat(errorMessageTemplate, errorMessageArgs));
        }
}

2. checkState   用作检查状态

　　public static void checkState(boolean expression) {
        if (!expression) {
            throw new IllegalStateException();
        }
    }

    public static void checkState(boolean expression, @Nullable Object errorMessage) {
        if (!expression) {
            throw new IllegalStateException(String.valueOf(errorMessage));
        }
    }

    public static void checkState(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) {
        if (!expression) {
            throw new IllegalStateException(Strings.lenientFormat(errorMessageTemplate, errorMessageArgs));
        }
    }

3.checkNotNull    检查参数是否不为空

@CanIgnoreReturnValue
    public static <T> T checkNotNull(T reference) {
        if (reference == null) {
            throw new NullPointerException();
        } else {
            return reference;
        }
    }

    @CanIgnoreReturnValue
    public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
        if (reference == null) {
            throw new NullPointerException(String.valueOf(errorMessage));
        } else {
            return reference;
        }
    }

    @CanIgnoreReturnValue
    public static <T> T checkNotNull(T reference, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) {
        if (reference == null) {
            throw new NullPointerException(Strings.lenientFormat(errorMessageTemplate, errorMessageArgs));
        } else {
            return reference;
        }
    }